Category Archives: Spiders

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Expiscor (20 May 2013)

This week’s Expiscor is coming to you on a holiday Monday across much of Canada. This is the day that many Canadians feel that the ‘warm season‘ has officially arrived. We can plant things in our garden without fear of frost; the lawn shall be mowed, the birds are busy, the butterflies are flying.

What is Expiscor? …it’s a weekly digest of discoveries from the world of entomology, biology, and so much more.

  • It seems that every week there’s a story about ‘dangerous spiders‘ – this week, Bug Girl wrote a post to help FIX THE INTERNET – in this case, to discuss a bogus spider poster.
  • On the topic of jumping spiders – they can make you look twice – WOW, WOW and WOW again. (thanks Alex Wild, for that photo, and permission to use it)

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  • Biodiversity under foot – great video about threats to soil biodiversity (thanks to my former MSc student, and recent PhD graduate, Zach for posting that link.
  • Fireflies: I always find the larvae of the Lampyridae beetles to be odd-looking, and I sometimes have trouble reconciling their habitus with adults.  This is a lot easer thanks to Derek Hennen for this lovely photo of an adult – check out that abdomen! (and thanks, Derek, for allowing me to use this photo)

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  • Scale it. This is VERY worth checking out. I personally like 10 to the power of -2.5
  • A worthy ordeal: Another great post from one of my heroes, Simon Leather – a terrific tradition in the British University system.
  • Lego geek-fest. Star Wars, LOTR, Arrested Development & so much more.
  • To finish, as usual, with some music. I’ve been a fan of Steve Earle for quite a long time, and his latest album (the Low Highway) does not disappoint. Here’s a video from one of the songs from that album. Worth a listen (and a good lesson in there, too)

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Expiscor (13 May 2013)

Start your week with some discoveries: from entomology to natural history, Academia & beyond! Expiscor – a weekly digest. (you can find past editions here).

  • In other entomology news, a paper about fatigue of insect cuticle. Yes, insects do wear out, eventually (mind you, it took 100,000 cycles before the wing samples failed!).
Photo by D. Llavaneras, reproduced here with permission.

Photo by D. Llavaneras, reproduced here with permission.

  • Hipsters – that was so last year. The current fad is clearly THRIPSTERS (again, Ainsley Seago show up in Expiscor!).
  • A milestone I’d rather we did not reach: Carbon dioxide levels pass 400 ppm. Not good news. So, I suppose I should not let my car idle while I stop in for groceries, right?
  • Muzzled Government scientists in Canada – here’s a must-read article on the topic from Maclean’s Magazine.  Here’s a quote from David Schindler: ‘They’re [the gov't] all for science that will produce widgets that they can sell and tax, but it’s clear that environmental scientists are lumped right down there with Greenpeace in their view’
  • Speaking of food, this photo essay has been around for a while, but worth a look – it’s all about how groceries for a week, from around the world.  Clearly quite a lot of us overeat.
  • Achoo! Allergy season is upon us here in the Montreal area – pollen counts are apparently ridiculously high this year (yes, you can get a ‘pollen report‘).  Here’s the hood of my car one morning last week:

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  • Where in the world am I?  Great little game using Google Street View. I spent a lot of time playing with this on the weekend – amazing to see what ‘clues’ tell you where you might be. Street signs, styles of the cars, electrical lines (above ground, or not?).
  • Here’s a nice idea: suspended coffee.  Buy an extra coffee for someone who may later come along and need a coffee but be unable to pay for it.
  • Good news for Dale Boyle (a guy with more than a few McGill connections). He’s a heck of a songwriter and that was recognized recently. Incidentally, he also sold me a guitar a few years back and that was a catalyst for me to start playing music again. Although this particular video doesn’t display his songwriting skills, it sure is lovely:

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The case of the missing genitalia: copulation costs for male spiders

This post is written by Chris Buddle (Associate Professor, McGill University). This article was originally published in “The Canadian Arachnologist” – a newsletter about Arachnology in Canada (this newsletter is no longer being published). 

Spider sex can be a dangerous and costly venture, the classic example being the (often) misunderstood act of sexual cannibalism (e.g., the black widow spider). However, many of the costs for males are not always so obvious: during copulation, the emboli of some male spiders may break off, which results in the male being unable to properly re-fill his palpal organ and mate again (Foelix 1996). Without this ability, the male’s future is essentially an early retirement. While sorting and identifying spiders for my dissertation research, I noticed that male Cybaeopsis euopla (a ‘hackledmesh’ weaver spider) seemed to frequently be missing one or both of their pedipalps.  Could this be another example of a copulation cost?

Looking to the literature, missing pedipalps are documented with some species – tiny males from the sexually dimorphic genus Tidarren (Theridiidae) will remove their own palps and this increases their running speed considerably (Ramos et al. 2004). Working with the same genus, Knofach and van Harten (2001) observed that females remove one of the male’s palps ‘after achieving genitalia coupling’. The female then proceeds to eat the male, while the detached palp acts as both a mating plug and continues to inseminate the female! Something similar happens with the species Nephilengys malabarensis and this fascinating biology was reported by science bloggers such as Ed Yong. In the wolf spider (Lycosidae) Pardosa milvina, frequent palpal losses were observed and effects on courtship and mating were studied by Lynam et al. (2006). Perhaps not surprisingly, these authors report that ‘intact males were less likely to be cannibalized and suffered fewer predatory attacks by females than autotomized males’.

With that background, I began counting the frequency of missing pedipalps for a sub-sample of the specimens of C. euopla. The objective was to assess the percentage of males were missing right, left, or both pedipalps and see if this related to phenology or other life-history events.

The samples came from a mixed-wood forest at the George Lake Field Station, located about 75 km NW of Edmonton, Alberta. This mature mixed-wood forest is dominated by trembling aspen and balsam poplar. Samples were collected using standard pitfall traps, and were part of several other projects on spider assemblages in mixed-wood boreal forests (e.g., see Buddle 2001).

Cybaeopsis euopla - lovely little spiders! (Photo by C. Buddle)

Cybaeopsis euopla – lovely little spiders! (Photo by C. Buddle)

Cybaeopis euopla (Amaurobiidae) (formerly Callioplus euoplus) is widespread in Canada, ranging from the Maritimes to the far north-west (Leech 1972). Males are about 3.5 to 5 mm in length, and are pale orange to light brown in colour. Specimens are typically collected from the leaf-litter of closed-canopy deciduous forests (Leech 1972; Buddle et al. 2000). From a sample of 653 male C. euopla, I found a total of 309 (or 47%) to be missing either one or both pedipalps. This is an impressive number, and essentially means that about half the males in the population are missing the very parts of their bodies that are required for reproduction. Of the 309 that were missing pedipalps, 124 were missing the left pedipalp, 97 were missing the right pedipalp, and 88 were missing both. In virtually all cases, the pedipalp was severed at the trochanter-femur joint. So the most plausible explanations for missing pedipalps are:

  • Pedipalp autotomy occurs during the act of copulation
  • The female may remove the pedipalps before, during or after copulation
  • C. euopla males may use their pedipalps in antagonistic courtship behaviours
  • Perhaps pedipalps are frequently used to grapple with aggressive prey, and are thus damaged.

It would be difficult to relate missing pedipalps to the act of copulation without detailed studies of courtship and copulation in C. euopla. However, the fate of pedipalps could be determined indirectly if the frequency of missing pedipalps increased during the reproductive period. The period of reproduction for ground-dwelling spiders, such as C. euopla, can be assessed from the peak activity period for male and female spiders, inferred from a passive sampling technique such as pitfall trapping. Using a larger data-set for male and female C. euopla collected by pitfall traps set at the George Lake Field Station, it is evident that males are most active early in the season (early May through the end of June) (Figure 1). Females were found throughout the spring and summer months over two years, with a slight increase in late June (Figure 1). These results generally agree with Leech (1972), who suggests May and June are the main periods of activity for C. euopla. Thus, it is inferred that this species will mate primarily in the spring in central Alberta.

Fig 1

The next step is to ask whether the frequency of missing pedipalps is related to the hypothesized mating period. This was done by calculating the average percentage of males with missing pedipalps as a function of sampling date (Figure 2). In both sampling years, the percentage of males with missing pedipalps increased as the season progressed (Figure 2). Although the sample size for July samples was low (12 individuals), the average number missing pedipalps was over 80%. Furthermore, the earliest sampling date in 1999 (6 May), which collected over 200 individuals, had the lowest average percentage of males with missing pedipalps (< 20%). These results indirectly suggest that as the season progresses, and the spiders mate, males begin to lose their pedipalps. I can therefore likely exclude the possibility that palpal loss is related to aggressive prey, and the explanation is likely related to courtship or copulation.

Fig 2

This small study has raised as many questions as it has answered, and there are certainly other explanations that I have failed to mention. I invite fellow Arachnologists to comment on the phenomenon of missing pedipalps in C. euopla, and in other species.  I suspect pedipalp loss is widespread, but seriously understudied. Given this importance of palps to the fitness of spiders, future research is certainly warranted.

References:

Buddle, C. (2001). Spiders (Araneae) associated with downed woody material in a deciduous forest in central Alberta, Canada Agricultural and Forest Entomology, 3 (4), 241-251 DOI: 10.1046/j.1461-9555.2001.00103.x

Buddle, C., Spence, J., & Langor, D. (2000). Succession of boreal forest spider assemblages following wildfire and harvesting Ecography, 23 (4), 424-436 DOI: 10.1034/j.1600-0587.2000.230405.x

Foelix, R.M. 1996. The Biology of Spiders. Oxford University Press.

Knoflach, B., & van Harten, A. (2001). Tidarren argo sp. nov. (Araneae: Theridiidae) and its exceptional copulatory behaviour: emasculation, male palpal organ as a mating plug and sexual cannibalism Journal of Zoology, 254 (4), 449-459 DOI: 10.1017/S0952836901000954

Leech, R. 1972. A revision of the nearctic Amaurobiidae (Arachnida: Araneida). Memoirs of the Entomological Society of Canada 84: 1-182.

Lynam, E., Owens, J., & Persons, M. (2006). The Influence of Pedipalp Autotomy on the Courtship and Mating Behavior of Pardosa milvina (Araneae: Lycosidae) Journal of Insect Behavior, 19 (1), 63-75 DOI: 10.1007/s10905-005-9008-x

Ramos, M. (2004). Overcoming an evolutionary conflict: Removal of a reproductive organ greatly increases locomotor performance Proceedings of the National Academy of Sciences, 101 (14), 4883-4887 DOI: 10.1073/pnas.0400324101

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Expiscor (19 April 2013)

Here’s  Expiscor -some discoveries I stumbled upon this week… (past versions can be found here)

  • World’s Biggest Butterfly Collection.  This video explores the amazing collection at London’s Natural History Museum.
  • Spiders, spiders, lovely spiders.  How about this image of a spitting spider by Chris Ruijter – STUNNING (thanks Alex Wild for directing me to Chris’ photos…)
A spitting spider, photo by Chris Ruijter (reproduced here, with permission)

A spitting spider, photo by Chris Ruijter (reproduced here, with permission)

  • The trees are speaking… this story describes how scientists listen to ultrasonic noise made by bubbles forming inside water-stressed trees (thanks Carly Ziter for that link)
  • More on the links between Art and Science.  The debate about “E.O. Wilson versus Math” inspired a discussion in my ecology class, but coincidentally, a friend of mine also pointed me to this truly lovely writing about Mathematics and the Arts (starts on page 55), written by Marston Morse in1959. Here is a quote from that piece:

            “…mathematics is the sister as well as the servant of the arts and is touched by the same madness and genius. This must be known.”

  • A passion for beetles: a retired researcher from Germany’s Federal Center for Meat Research in Bavaria has a lovely collection of Coleoptera, 6,000 species at over 30,000 individuals. Now that’s a hobby! (thanks Bug Girl for the tweet about that story)
  • To finish, glad to see that Entomologists are out there correcting bad taxonomy.  Here, Ainsley Seago (aka @AmericanBeetles) does some fine work (and it was given a stamp of approval by Taxonomy Hulk – yes, we do need him, too!)

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Spiders as catalysts for ecosystem development

It is well known that spiders are effective at dispersal and colonization, in part because of their ability to ‘balloon‘ – small spiders (i.e., immature specimens, or adults of species that are small) will release a strand of silk and let the wind pick them up and carry them far distances.  This passive ability to disperse has served spiders well, and enabled them to be among the first animals to colonize new habitats.  For example, after the eruption of Mount St Helens, the depopulated Pumice Plain was re-colonized over time, and biologists kept an eye on what was dropping from the skies.  Not surprising (to me!) was that spiders represented a lot of this ‘aerial plankton‘ – Crawford et al. (1995) reported that spiders represented “23% of windblown arthropod fallout and contributed 105 individuals per square meter“.

A spider about to launch! Photo by Bryan Reynolds, reproduced here with permission. Please visit his work!

A spider about to launch! Photo by Bryan Reynolds, reproduced here with permission.

Many, many people have recognized this amazing ability of spiders to get to places effectively and quickly.  During his voyages on the HMS Beagle, Darwin observed and commented on this. He noticed spiders landing on the ship when they were far offshore.  Here’s a lovely quote:

      These, glittering in the sunshine, might be compared to diverging rays of light; they were not, however, straight, but in undulations like films of silk blown by the wind.

-Charles Darwin, Voyage of the Beagle, 1832

A wonderful paper titled “Distribution of Insects, Spiders, and Mites in the Air” (Glick 1939) also discusses aerial plankton. In this work, Glick reports on how a plane was used to collect arthropods in the skies – this was done by modifying the plane so it had a collection net attached to it.  Spiders were among the most commonly collected taxa, and were found up to 15,000 ft in altitude.   Glick followed this up with work published in 1957, and spiders were again reported as common aerial plankton.

Convinced?  Spiders really are everywhere and can get anywhere – from dominating the tundra, to floating far above as tiny eight-legged aeronauts.

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This takes me (finally) to the point of this post, and some reflection about a paper by Hodkinson et al. (2001), titled “What a wonderful web they weave: spiders, nutrient capture and early ecosystem development in the high Arctic – some counter-intuitive ideas on community assembly”.  In this work, the authors provide some data about aerial plankton in a series of sites representing different stages of succession in Midtre Lovénbreen – a ‘small valley’ glacier in Spitsbergen (a Norwegian high Arctic Island).   This forum paper was meant to present an idea about ecosystem development in the Arctic, with a focus on spiders and other aerial plankton and their relationship to nutrients.

  • Spiders are among the first to arrive due to their amazing abilities at dispersal and colonization.
  • Many spiders will just die, and their sad, little bodies will decompose and leave behind nutrients.
  • Many of the spider species that arrive will build webs, and the silk contains many nutrients. Regardless of whether the silk successfully captures prey, the silk will eventually be a hot-spot of nutrients.
  • A lot of other aerial plankton will hit these webs – this will include other arthropods (Hodkinson et al. rightfully point out the importance of Chironomids, or midges, as key prey for spiders in the north) and these prey may or may not be eaten by spiders.  The aerial plankton also includes other ‘debris’ that would be floating around (fungal spores, dirt, etc).  The webs capture all these goodies, and act as a concentrated area for a growing soup of nutrients.
  • The spider webs will collect moisture.  In Arctic systems, dry polar-deserts, and many other newly created habitats, the accumulation of moisture is rather essential for continued ecosystem development.

Taken together, Hodkinson et al. (2001) argue that spiders and their webs represent little pockets of concentrated nutrients in landscapes that are void of much other life.  These hotspots could be catalysts for ecosystem development in systems that are starting from scratch.  I really like this idea – not only does is stir up the imagination (little spiders gently falling from the sky, landing on habitat never before touched by animals, and providing the start of an ecosystem…), it really makes some biological sense.  Ecosystem development requires nutrients and substrates – of course, these would both be available without spiders, but our eight-legged friends are helping move things a long a little more quickly.

The paper by Hodkinson et al. has been cited less than I would have expected.   Although they don’t provide any experimental data, their ideas are interesting and relevant and should be studied in detail. Recently, a few papers have come out that are taking the ideas to the next level.  Konig et al. (2011) studied arthropods of glacier foregrounds in the Alps. They found that although Collembola and other ‘decomposers’ are quite important in early successional stages, overall, generalist predators (including spiders) were dominant and using stable isotope analyses, they showed that these generalist predators often ate each other – an interaction known as intraguild predation.

I often discuss Hodkinson et al.’s (2001) paper in lectures, and invariably I get the question “If spiders are first to arrive, what do they eat?“. I typically answer that spiders eat other spiders, and it’s reassuring to see literature that supports this claim.  In turn, intraguild predation itself contributes further to the accumulation of nutrients (more sad, little spider bodies littering the landscape…).

Placing this work in a more general framework, these ideas are pointing to the increased importance of predators in overall nutrient dynamics in ecosystems. I was thrilled to see a paper by Schmitz et al. (2010) that argues “predators can create heterogeneous or homogeneous nutrient distributions across natural landscapes“. Bingo. This is exactly what Hodkinson et al. were arguing – predators, such as spiders, can arrive quickly to an area, and in the context of newly formed ecosystems, may provide a hotspot for nutrients in an otherwise desolate landscape.

Although the Hodkinson et al. paper is over a decade old, it’s still relevant, and quite important. I suspect that if more newly created habitats are studied in detail, spiders will indeed prove to be catalysts for ecosystem development.

References:

Crawford, R., Sugg, P., & Edwards, J. (1995). Spider Arrival and Primary Establishment on Terrain Depopulated by Volcanic Eruption at Mount St. Helens, Washington American Midland Naturalist, 133 (1) DOI: 10.2307/2426348

Hodkinson, I., Coulson, S., Harrison, J., & Webb, N. (2001). What a wonderful web they weave: spiders, nutrient capture and early ecosystem development in the high Arctic – some counter-intuitive ideas on community assembly Oikos, 95 (2), 349-352 DOI: 10.1034/j.1600-0706.2001.950217.x

König, T., Kaufmann, R., & Scheu, S. (2011). The formation of terrestrial food webs in glacier foreland: Evidence for the pivotal role of decomposer prey and intraguild predation Pedobiologia, 54 (2), 147-152 DOI: 10.1016/j.pedobi.2010.12.004

Schmitz, O., Hawlena, D., & Trussell, G. (2010). Predator control of ecosystem nutrient dynamics Ecology Letters, 13 (10), 1199-1209 DOI: 10.1111/j.1461-0248.2010.01511.x

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A special thanks to Bryan Reynolds for permission to use his photograph of the dispersing Pisaurid spider.  Please visit his work here.

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Where are all the Arachnologists? (and why you should care)

Canada is a big country, with an amazing diversity of habitats, from the temperate rainforests of Vancouver Island, to the polar deserts on Ellesmere Island.  We are a country that harbours thousands of Arachnid species (yes, our eight-legged friends!).  Some examples: the Yukon Territory hosts over 300 spider species and over 150 species of Oribatid mites; Quebec is home to well over 600 spider species.  The Alberta Biodiversity Monitoring Institute has documented over 200 species of Sarcoptiformes mites from a relatively few number of sites in Alberta, and their work is far from complete.  The Canadian National Collection of Insects and Arachnids in Ottawa has one of the best spider and mite collections, world-wide.

A beautiful jumping spider. Photo by C. Ernst, reproduced here with permission.

A beautiful jumping spider. Photo by C. Ernst, reproduced here with permission.

The general public is fascinating by Arachnids: my post titled ‘Spiders do Not Bite‘ continues to get hundreds of hits every week.  We link comic-books and superheroes to Arachnids (even if the anatomy of spiderman is all wrong…).  Spider silk is used to make dresses, violin strings, and has potential in pest control.  There are invasive spider species that go unnoticed, yet may affect native species – as Bednarski, et al (2010) have documented in Maine.  Spiders continually show up in grocery stores and cause alarm and fear (although mostly not warranted..).  People are often picking ticks off their pets, or hearing about lyme disease.

Everyone has a story to share about Arachnids.

Recently, the Class Arachnida was a lunchtime topic of discussion in the lab. This discussion was in part prompted by an email I received from Leslie Brunetta. She asked the question about how we can promote Arachnology in University education.  One way to do this would be for Arachnologists to agree to deliver guest lectures in organismal biology classes, and this got us into a discussion about how many people get paid to work on Arachnology in Canada.

I tried to estimate the number of people in Canada who spend a significant portion of their time getting paid to do things with Arachnids – and I consulted a lot of colleagues to get this done.  This would include academics with a research focus on Arachnids (from behavioural ecology to biodiversity science), and government scientists working on Arachnids (from systematics through to the use of mites as biological control agents).  This does not include graduate students, nor does it include people working on short-term contracts.  I estimate that fewer than 20 people are paid to work on Arachnids in this country. This is truly astounding and astonishing.  Arachnids include two Orders that are among the most diverse on the planet: combining the Acari (mites & ticks) and Araneae (spiders) gives you estimates of well over 85,000 described species, globally.  There are only a handful of Insect Orders that are higher.

Let’s revisit why EVERYONE should care about Arachnids and why Canada ought to have more Arachnologists: 

Spiders are key predators in agroecosystems (the classic paper by Riechert & Lockley 1984 is quite relevant!). Spiders eat mosquitoes, including those that can be vectors for malaria (Nelson & Jackson 2006) .  Spiders are key prey for highly valued vertebrates (Gunnarsson 2007).  Spiders can be medically important – their venom has remarkable potential for drug development (Rates et al. 2011).

Mites are everywhere – they play critical roles in decomposition of organic matter (Kampichler & Bruckner 2009). Plant-feeding mites are economically important for dozens of crops.  Follicle mites are in our heads (Elston 2010).

Ticks can transmit diseases that are very important for human health and well being (Sperling & Sperling 2012). Ticks can hurt our beloved pets (Blagburn & Dryden 2009).  Ticks can be harmful for wildlife populations (Addison et al. 1994).

Need more convincing?

Arachnids are stunningly beautiful; they are among the ‘small and obscure’ creatures most worthy of study. In addition to mites, ticks and spiders, we can’t forget about Opiliones, Pseudoscorpiones, Scorpiones and other Orders… Arachnids should adored as much as Pandas, or the Mona Lisa.

8 Oribatid mites scaled to a 12 pt Times Roman period (0.5 mm dia.). Photo by D. Walter, reproduced here, with permission. You should visit his blog.

8 Oribatid mites scaled to a 12 pt Times Roman period (0.5 mm dia.). Photo by D. Walter, reproduced here, with permission. You should visit his blog.

CANADA: THIS IS A CRISIS!  We must find a way to ensure Arachnologists get paid to do Arachnology in Canada.  The most obvious place to point is the CNC.  It is unacceptable that a spider taxonomists has yet to be hired to maintain that spider collection.  We should be embarrassed.  Taxonomists are needed in Canada, especially for dominant arthropod groups.  The Canadian Council of Academics makes this point quite clearly in their report on Canadian Taxonomy:

     Job openings in taxonomy have virtually ceased and research funding is stagnant.  Canada’s international contribution to new species descriptions has fallen from 6th in the 1980s to 14th in the 2000s. 

Oh Canada. Where are your Arachnologists?

Oh Canada. Where are your Arachnologists?

I realize that many other taxonomic groups remain understudied – However, I am discussing an entire Class of animals!  Could you imagine if I were discussing Mammalia, or Reptilia, or Insecta?  There would be an uproar.

Let us work to fix this.  Let’s train excellent Arachnology graduate students, let’s lobby Departmental Chair, Deans, Bureaucrats in Government, members of Parliament, and whoever else will listen.  MUST Listen.

Our eight-legged friends need our help.

References

Addison, E., McLaughlin, R., & Broadfoot, J. (1994). Growth of moose calves infested and uninfested with winter ticks Canadian Journal of Zoology, 72 (8), 1469-1476 DOI: 10.1139/z94-194

Blagburn BL, & Dryden MW (2009). Biology, treatment, and control of flea and tick infestations. The Veterinary clinics of North America. Small animal practice, 39 (6) PMID: 19932369

Danks VH and JA Downes. 1997. Insects of the Yukon. Biological Survey of Canada.

Gunnarsson, B. (2007). Bird Predation On Spiders: Ecological Mechanisms And Evolutionary Consequences Journal of Arachnology, 35 (3), 509-529 DOI: 10.1636/RT07-64.1

Elston, D. (2010). Demodex mites: Facts and controversies Clinics in Dermatology, 28 (5), 502-504 DOI: 10.1016/j.clindermatol.2010.03.006

Kampichler, C., & Bruckner, A. (2009). The role of microarthropods in terrestrial decomposition: a meta-analysis of 40 years of litterbag studies Biological Reviews, 84 (3), 375-389 DOI: 10.1111/j.1469-185X.2009.00078.x

Nelson, X., & Jackson, R. (2006). A Predator from East Africa that Chooses Malaria Vectors as Preferred Prey PLoS ONE, 1 (1) DOI: 10.1371/journal.pone.0000132

Rates B, Verano-Braga T, Santos DM, Nunes KP, Pimenta AM, & De Lima ME (2011). From the stretcher to the pharmacy’s shelf: drug leads from medically important brazilian venomous arachnid species. Inflammation & allergy drug targets, 10 (5), 411-9 PMID: 21824079

Paquin, P.  &  N. Dupérré 2006. The spiders of Québec: update, additions and corrections. Zootaxa 1133: 1-37.

Riechert, S., & Lockley, T. (1984). Spiders as Biological Control Agents Annual Review of Entomology, 29 (1), 299-320 DOI: 10.1146/annurev.en.29.010184.001503

Sperling, J., & Sperling, F. (2012). Lyme borreliosis in Canada: biological diversity and diagnostic complexity from an entomological perspective The Canadian Entomologist, 141 (06), 521-549 DOI: 10.4039/n08-CPA04

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Where did all the spiderlings go? A story about egg-sac parasitism in Arctic wolf spiders

This week we are in a deep freeze in the Montreal area, so it seems somewhat fitting to discuss Arctic spiders.  I’ve discussed the life-history of Arctic wolf spiders (Lycosidae) before, specifically in the context of high densities of wolf spiders on the tundra.    Much of this work was done with my former PhD student Joseph Bowden.  The latest paper from his work was published last autumn, and was titled ‘Egg sac parasitism of Arctic wolf spiders (Araneae: Lycosidae) from northwestern North America‘. In this work we document the rates of egg sac parasitism by Ichneumonidae wasps in the genus Gelis.  These wasps are fascinating, and we have found them to be very common on the tundra.  There are often multiple wasps in a single egg sac, and as is typical with Gelis, they leave nothing behind: all eggs within an egg sac are consumed.  After fully developed, the adult wasps pop out of the egg sac; the Gelis adults we encountered had both winged forms and wingless females, the latter superficially resembling ants.

A Gelis emerging from a wolf spider egg sac. Photo by Crystal Ernst, reproduced here with permission.

A Gelis emerging from a wolf spider egg sac. Photo by Crystal Ernst, reproduced here with permission.

The rates of parasitism of Pardosa egg sacs (by Gelis) were, at some sites, extremely high.  In some cases over 50% of the wolf spider egg sacs were parasitized.  Stated another way,  half of all the females encountered with egg sacs had zero fecundity because the female was  carrying around wasps within the egg sac instead of spider eggs.

It’s quite interesting to think about these wingless Gelis females: after emerging from egg sacs, they end up wandering around the tundra in search of hosts.  Spiders with egg sacs must be encountered frequently enough for the wasps to grab on to a passing wolf spider in order to parasitize the egg sac.  Recall, densities of wolf spiders can be very high in the Arctic (4,000 per hectare, at least).  Hmmm…. this is all starting to fit… high densities of wolf spiders support high rates of egg parasitism and these wasps can ‘afford’ to be wingless since their hosts are frequently encountered:  an interesting feedback loop!   We can also speculate about large-scale gradients in diversity – many Ichneudmonidae show high diversity in northern regions.  Within Gelis, it’s a good bet that they will find many suitable spider hosts in these environments.

Looking down the microscope - all those Gelis!

Looking down the microscope – all those Gelis!

So, how extreme are these rates of egg parasitism?  Looking at some of the literature, there are certainly a number of papers about  wasps that parasitize spider egg sacs.  Cobb & Cobb (2004) studied two Pardosa species in Idaho, and recorded a egg parasitism rate of about 15% (by Gelis wasps and wasps in the genus Baeus [Sceleonidae]). Van Baarlen et al (1994) studied egg parasitism in European Linyphiidae spiders and their maximum rates of parasitism were about 30%.   Finch (2005) did a detailed study of four spiders species (non-Lycosidae) and rates of egg parasitism varied between 5% up to as high as 60% in an Agroeca species.

Our documented parasitism rates for Arctic wolf spiders are certainly quite high (for Lycosidae), but not out of the range of other published studies for non-Lycosidae.  I do wonder whether we will continue to find high egg parasitism rates if more species were examined in detail – certainly a fertile area of study.  Related to this, what are the population-level consequences of this interaction?  What is the relationship between spider densities and parasitism rates?  Although Joe and I did try to speculate on this, our data are preliminary – again, a key area for future research.

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In the Arctic context, we will continue to uncover fascinating food-web dynamics.  Our research group has already been thinking seriously about this – Crystal Ernst has written a nice post about the idea of an ‘inverse trophic web’ (i.e., predator-dominated) in the Arctic, and a fair amount of my future research will pursue this avenue of research.

Pique your interest…?  Why not think about graduate school in my lab, and study Arctic arthropod biodiversity?

References:

Bowden, J., & Buddle, C. (2012). Egg sac parasitism of Arctic wolf spiders (Araneae: Lycosidae) from northwestern North America Journal of Arachnology, 40 (3), 348-350 DOI: 10.1636/P11-50.1

Cobb, LM & Cobb VA (2004). Occurrence of parasitoid wasps, Baeus sp and Gelis sp., in the egg sacs of the wolf spiders Pardosa moesta and Pardosa sternalis (Araneae: Lycosidae) in southeastern Idaho. Canadian Field Naturalist 118(1); 122-123.

Baarlen, P., Sunderland, K., & Topping, C. (1994). Eggsac parasitism of money spiders (Araneae, Linyphiidae) in cereals, with a simple method for estimating percentage parasitism of spp. eggsacs by Hymenoptera Journal of Applied Entomology, 118 (1-5), 217-223 DOI: 10.1111/j.1439-0418.1994.tb00797.x

Finch, O. (2005). The parasitoid complex and parasitoid-induced mortality of spiders (Araneae) in a Central European woodland Journal of Natural History, 39 (25), 2339-2354 DOI: 10.1080/00222930500101720

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Fear factor: spider silk reduces plant damage

Today I am excited to report on research published with Ann Rypstra, a most wonderful person and exceptional spider ecologist.  Here’s the take home message from our paper, titled  ”Spider silk reduces insect herbivory” (Rypstra & Buddle 2013):

In the presence of spider silk, insect herbivores eat less plant material  - and the spider doesn’t have to be around to see this effect!

A spider’s web, made with silk. Photo courtesy of M. Larrivee (reproduced here, with permission)

Here’s a plain-language summary of the research:

Spiders are important in agricultural systems because they eat many insect pests that in turn eat valuable crops.  Spiders also leave behind silk as they move through an agricultural field – sometimes this silk is there because it was part of a web that was constructed to catch prey, or sometimes spiders leave silk in the form of a ‘drag-line’ – a kind of silk that acts as a safety-line for a spider.  Whatever the means, the agricultural landscape contains plants, their insect pests, spiders and spider silk.  In this work, we wondered whether  silk, in the absence of a spider, would still cause the insect pests to be wary, and feed differently than if there was no spider silk in their environment.  

We used laboratory and field-based experiments for this research, and we used two pest species – the Japanese beetle and the Mexican bean beetle.  These pests were allowed to eat either leaflets or whole plants of bush-style snap beans.  The plants or leaflets were either left alone, or were adorned with five strands of spider silk or with five strands of silkworm silk.  We included the silkworm silk (i.e, produced from the silkworm moth) because we were curious about whether the beetles might respond to ANY silk instead of silk produced specifically by spiders.  To extract the spider silk, we allowed a long-jawed orb-web spider to hang from its drag-line, and we wound its silk around a stick as the spider bobbed up and down – in this way we could get enough silk for the experiments. We found that when spider silk was on the plants, the insects inflicted less damage compared to when there was no silk.  The silkworm silk also caused the insects to feed less, but the effect with silkworm silk was less than with spider silk.  We also wondered whether this response could just be because the silk got in the way of the beetles, and so we did some experiments with human hair, and a strand of kevlar – these are both ‘silk-like’ strands but since they did not come from an insect or spider, would only represent the physical nature of the silk rather than have any other chemicals or smells from the silk produced by a insect or spider.  This additional experiment showed us the same results: the insect pests still ate less when on plants containing silkworm silk or spider silk compared to those with the kevlar or human hair.  

All these experiments, combined, tell us that there is something very special about spider silk, and it causes pest insects to eat less plants.  In ecology this is dubbed an ‘indirect’ effect – the spiders do not have to eat a pest insect to cause it to change its behaviour! It is also called a ‘non-consumptive effect’ – meaning the effect of the spider on its prey is not through the act of eating the prey, but rather by changing prey behaviour by other means.  This work is fascinating because it shows that spiders have a much more important role in agricultural systems than we realized before: spiders do not have to be present to cause insects pests to eat less – as long as they were there, and produced silk as they moved through their environment, their potential prey will live in a ‘landscape of fear’.  Or, the insect pest is living in fear of spiders because of their silk. 

Here is a more technical summary, placed within a broader ecological context:

Tetragnatha – a long-jawed orb-web spider. Photo by Lee Jaszlics, reproduced here with permission

The pest insects (the beetles) in our study system recognize the silk is coming from a potential predator (the spider), and this means they alter their behaviour, or LIVE IN FEAR!  This work fits within the broader literature about the landscape of fear (e.g. see Laundré et al. 2012), or ecology of fear sensu Brown et al. (1999). The idea here is that prey are shifting their behaviours depending on predators, and so the prey’s overall ‘landscape’ is peaks and valleys related to the strength and type of interactions (direct or indirect) caused by the predator.  To anthropomophize this even more: fear induces behavioural changes in prey; they are scared and this fear has real and measurable effects.

Although a lot of this kind of research is with vertebrates, there are some interesting examples from the arthropod world.  One recent example is by Hawlena et al. (2012) – in this work, grasshoppers that were raised in an environment of fear (via continual exposure to spiders whose chelicerae were glued shut) had different Carbon:Nitrogen ratio in their bodies relative to controls, and this affected plant litter decomposition.  So, the ‘fear factor’ changed the elemental composition of grasshopper’s bodies and eventually this affected the decomposition process!  In Hlivko & Rypstra’s (2003) work, a leaf-eating beetle, when exposed to a range of cues produced by spiders (this included feces, silk and other chemicals) ate less plant biomass compared to controls, and the strongest effect was from cues of the largest spider.   Within the context of fear – the largest (and presumably the most feared) spider, can elicit a response in its prey which results in an affect on plant biomass.  Our paper is taking this one more level, and focuses on the silk as a key ‘cue’ that induces the behavioural change in the prey.

Our results show that insect pests that feed on plants in agroecosystems may be living in a landscape of fear that is brought on by one of the most common substances produced our eight-legged friends…the silk.  This silk acts as an important cue for the insect pests and they eat less plant material because of this.   This research also shows the added value of spiders in agroecosystems; conservation of spiders, or even habitat manipulations to encourage spiders to live in agroecosystems, could have many pay-offs.

The study species in our research: Tetragnatha (photo courtesy of M. Larrivee, reproduced here with permission)

Thanks to Max Larrivee and Lee Jaszlics for permission to use their wonderful photographs!

References:

Brown, J., Laundré, J., Gurung, M., & Laundre, J. (1999). The Ecology of Fear: Optimal Foraging, Game Theory, and Trophic Interactions Journal of Mammalogy, 80 (2) DOI: 10.2307/1383287

Hawlena, D., Strickland, M., Bradford, M., & Schmitz, O. (2012). Fear of Predation Slows Plant-Litter Decomposition Science, 336 (6087), 1434-1438 DOI: 10.1126/science.1220097

Hlivko, J., & Rypstra, A. (2003). Spiders Reduce Herbivory: Nonlethal Effects of Spiders on the Consumption of Soybean Leaves by Beetle Pests Annals of the Entomological Society of America, 96 (6), 914-919 DOI: 10.1603/0013-8746(2003)096[0914:SRHNEO]2.0.CO;2

Laundre, J., Hernandez, L., & Ripple, W. (2010). The Landscape of Fear: Ecological Implications of Being Afraid~!2009-09-09~!2009-11-16~!2010-02-02~! The Open Ecology Journal, 3 (3), 1-7 DOI: 10.2174/1874213001003030001

Rypstra, A., & Buddle, C.M. (2012). Spider silk reduces insect herbivory Biology Letters, 9 (1), 20120948-20120948 DOI: 10.1098/rsbl.2012.0948

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Spider cakes!

My graduate students are a very talented bunch – they are intelligent, creative, and have a good sense of humour.  Some of our lab group celebrated birthdays recently, and in honour of this, we had two cakes earlier this week.  The first, made by MSc student Sarah Loboda, is the VERY BEST SPIDER CAKE I have ever seen (or eaten!).  Check this out:

Spider Cake!

Of course, let’s discuss how anatomically correct that cake is!  Two body parts, pedicel, eight legs (coming from the cephalothorax, of course), and a bunch of eyes.

Spider cake! (eyes0

As you may know, most spiders in Canada have eight eyes, but since some do have six, I find it quite acceptable that this spider has six eyes.  Furthermore, not all spider eyes are identical so it is appropriate to have two kinds represented on the cake.  Well done, Sarah.

And in case that STUNNING MASTERPIECE isn’t enough, another student (Dorothy Maguire)  made a cake that is a very good approximation for the female epigynum of wolf spiders in the genus Pardosa.

Pardosa epigynum

And not just any Pardosa:  this is diagnostically similar to one of the species that graduate student Katie Sim is working on!  Incredible!

….want some proof – look at this image, taken from Dondale & Redner’s text on the Lycosidae of Canada.  Enough said.

Pardosa concinna epigynum

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The laboratory mascot is growing older, just like me.

Time marches on.

In my laboratory, I can judge the years by the growth of our lab’s mascot, a Chilean Rose-hair tarantula named “Harriet” (but who also goes by the name of Grillonthosaur).  I was away last week, but when I returned to the laboratory on Monday morning, my students were excited to tell me that Harriet is a little bigger than before I left.  She moulted, and now has a shiny new coat.

Our lab mascot, with her shiny new coat!

The story of Harriet is kind of amazing.  Before Harriet was our laboratory’s mascot, she was the pet of an enthusiastic undergraduate student at McGill.  This student loved entomology, and did a project in my laboratory about four months after I started as a shiny-new tenure-track assistant professor.   When this student left Montreal, she gave Harriet to me since she could not take the spider with her at the time.  That was in the winter of 2003, and Harriet was already several years old then.  Harriet is, therefore at least 13 years old and shows no signs of slowing down.

Harriet’s old ‘skin’.

Harriet has seen a lot of changes, and been a passive observer of quite a few graduate student research projects.  I am also growing older – I just turned 40 this past weekend.  I am pleased to report that I don’t seem to be showing signs of slowing down either.

(by the way, the undergraduate student I referred to left McGill for a MSc in British Columbia followed by a PhD in Australia.  She, like Harriet, is doing very, very well!)