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Spider Diversity at the Morgan Arboretum

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Natural History of Spiders

Arachnida is an extensive class of arthropods recognized mainly by their eight legs, lack of antennae and carnivorous lifestyle, according to the Encyclopaedia Britannica Online (2015). This class encompasses scorpions, mites, daddy long legs and spiders. Spiders belong to the order Araneae, which includes over 114 families and over 45,732 species reported today (World Spider Catalog, 2015). Spiders, though small, play important ecological roles in the ecosystems in which they reside. Their presence, or lack thereof, can be a critical determinant in insect population and consequently impact plant and animal life alike.

Funnel-web spider at night

Funnel-web spider at night

True spiders have opposite fangs that cross when closed and include all the familiar spiders, except tarantulas which have parallel fangs (Foelix, 2011). Additionally, true spiders are all capable of producing silk within abdominal glands and extract it using a pair of agile spinnerets (Turnbull, 1973). They all use their silk to some degree, whether it be to enclose their eggs within a silk cocoon, create a web or nest, or capture prey.

Anatomy of a "True Spider"

Anatomy of a “True Spider”

Common spider families in Saint-Lawrence Lowlands

The Morgan Arboretum, situated in the town of Sainte-Anne-de-Bellevue, is made up of both forest and grasslands. Within a small spatial range of this reserve, spider diversity can be quite extensive. Below, we profile several families common to the Saint-Lawrence lowlands, which can be observed in the Arboretum. Most of these spiders thrive in the spring and summer months, but many persist into fall.

Family Araneidae – Orb weavers

Compared to other spiders that spin flat orb webs, Araneidae is the family with the most species (Bradley, 2012). Orb weavers include 3,096 species overall (World Spider Catalog, 2015), of which 31 can be found in Quebec (Dupérré, Paquin, 2003). These spiders can be found almost anywhere: cellars, mines, grasses, or forests (Dondale, 2003).  Most are large and colorful, and have round bodies (Bradley, 2012). Orb weavers normally have three claws on each leg, the third claw is short and untoothed which allows the spider to hold on to its webs (Dondale, 2003). These spiders sense prey with web vibrations. As soon as the prey gets caught in the web the spider wraps the prey in a silk cocoon (Bradley, 2012). Their web-weaving includes four main parts: first, the spiders build the basic structure in a physical limit, after that they attach the center of the web to its outside limits using lines of silk, next they make  the temporary spiral, and finally, they replace the spiral with a sticky version, to capture prey (Dondale, 2003).

Female Argiope Trifasciata (Araneidae) resting in her web

Female Argiope Trifasciata (Araneidae) resting in her web

Family Thomisidae – Crab spiders

This family is made up of 2,155 species (World Spider Catalog, 2015), 32 of which can be found in Québec (Dupérré, Paquin, 2003). Their name is due to their crablike posture and movement. The abdomen is “saclike” and is softer than the carapace and sternum found on the cephalothorax (Dondale and Redner, 1978). The dorsal side may have a uniform color, or two lines of a different color, like in Misumena vatia (below). Their colors can be very bright, because crab spiders often capture pollinators. Some may even change color according to the surface they are on (Dondale and Redner, 1978).

Misumena vatia

Misumena vatia

Family Salticidae – Jumping spiders

This family is the largest with 5,841 named species (World Spider Catalog, 2015), 43 of which are found in Quebec (Hutchinson, 2003). They are easily recognizable by the horizontal alignment of four forward-facing eyes and huge distinctive median eyes (Bradley, 2012). These spiders are known for exhibiting intelligent behavior, including elaborate learned behaviors used for hunting their prey (Bradley, 2003). Most jumping spiders are active during the day, possess color vision, and are colorful. Many of these spiders are known for complex courtship rituals that involve movement and their colorful bodies (Bradley, 2012).

Jumping spider (Salticidae)

Jumping spider (Salticidae)

Family Lycosidae – Wolf spiders

Wolf spiders are one of the most widespread spider families, with 53 identified in Quebec (Hutchinson, 2003) and approximately 2,403 worldwide (World Spider Catalog, 2015). They are found in all habitats. The unusual arrangement of their eight eyes in what looks like three consecutive rows makes them easily recognizable and possess excellent vision (Bradley, 2012). Their good eyesight is employed during their mating rituals (Bradley, 2012). Depending on the species, wolf spiders can be active during the day or at dawn and dusk (Bradley, 2012). As they forage, they make use of a dragline, which is the laying down of a silk line that can serve as communication means between different individuals of the species (Bradley, 2012). Most of these spiders are ground hunters, building burrows, and waiting for prey instead of chasing it down (Bradley, 2012).

Our research

Our research is aimed at answering the following question: How does spider diversity differ in the vertical stratification of grasslands along the forest edge of a mixed deciduous forest at the Morgan Arboretum?

Spider collection can be done in multiple ways (Turnbull, 1978). This experiment uses both pitfall traps and sweep nets. Our pitfall traps produced little data in contrast to the sweeping, which may be due to heavy rain showers during the time the traps were set, or to soil settling down around the traps, creating an elevated ledge out of the cup lip, onto which spiders would not climb.

Sweep net method:

Each pitfall trap was filled with antifreeze diluted with water to prevent the liquid from freezing if the temperature reached below zero

Each pitfall trap was filled with antifreeze diluted with water to prevent the liquid from freezing if the temperature reached below zero

The experiment lasted 3 weeks. On October 5th, we located our site and swept the grassland. On October 13th, 45 pitfall traps were set. On October 19th the pitfall traps were collected and a second sweep took place. Sweeping three weeks apart in the rapidly changing temperature of autumn in Quebec resulted in a decrease of the number of spiders collected during the second sweep.

Picture1

As we started analyzing our samples in the lab with microscopes, we realized that the identification of spider families and species is quite challenging. There are numerous species to choose from, and some identifications even require internal organ analysis which we cannot perform. To help this situation we grouped spiders into over 30 types (morphospecies) based on their appearances and differentiable characteristics.

Many different species collected during this study

Many different species collected during this study

Overall, 119 spiders were classified from the first sweeping, 81 from the second sweeping and 25 from the traps. Additionally, nine spiders were unidentifiable due to severed body segments caused by decomposition within the antifreeze solution.

 Works Cited

Bradley, Richard A. “FAMILY LYCOSIDAE • Wolf Spiders.” Common Spiders of North America. : University of California Press, 2013-05-23.California Scholarship Online. Web. 28 Oct. 2015 http://california.universitypressscholarship.com/view/10.1525/california/9780520274884.001.0001/upso-9780520274884-chapter-35

Bradley, Richard A. “FAMILY SALTICIDAE • Jumping Spiders.” Common Spiders of North America. : University of California Press, 2013-05-23. California Scholarship Online. Web. 28 Oct. 2015.http://california.universitypressscholarship.com/view/10.1525/california/9780520274884.001.0001/upso-9780520274884-chapter-52.

Buddle, C. M., et al. (2006). “Arthropod responses to harvesting and wildfire: Implications for emulation of natural disturbance in forest management.” Biological Conservation 128(3): 346-357. Web. http://www.cfs.nrcan.gc.ca/bookstore_pdfs/25952cannotpostonline.pdf

Dondale, C. D., “Orb-Weaving Spiders of Canada and Alaska”. Ottawa, ON, CAN: NRC Research Press, 2003. ProQuest ebrary. Web. 28 October 2015.

Dondale, Charles D, and James H. Redner. “The Crab Spiders of Canada and Alaska: Araneae: Philodromidae and Thomisidae”, 1978. 200p. Print.

Foelix R. F, Biology of spiders, third edition, New York: Oxford University Press, 2011,419 p, Print,

Hutchinson, Raymond. “L’étude des araignées (Araneae) au Québec–le point et perspectives.” Le Naturaliste canadien 127.1 (2003): 24-31.Web. 27 October 1015. http://wsc.nmbe.ch/statistics/

Paquin P and Dupérré N, Association des entomologistes amateurs du Québec, Guide d’identification des araignées (Araneae) du Québec, Fabreries. Supplement 11. 2003. 259 p. Print.

Turnbull AL. “Ecology of the true spiders (Araneomorphae)”. Annual review of entomology, Volume 18. 1973.

“Arachnid”. Encyclopaedia Britannica. Encyclopaedia Britannica online. Encyclopedia Britannica Inc., 2015. Web. 27 oct. 2015.

“Currently Valid Spider Genera and Species (2015-10-29)”. World Spider Catalog, by World Spider Catalog Association. Last update 2015-10-29. 20 Oct 2015. Web. http://wsc.nmbe.ch/statistics/

“True Spiders (Suborder Araneomorphae)”. iNaturalist. July 08, 2015. Web. 28 Oct. 2015. http://canada.inaturalist.org/taxa/120474-Araneomorphae

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8 comments on “Spider Diversity at the Morgan Arboretum

  1. Thanks for writing this – as you know, I like spiders quite a bit! Did you notice any patterns in your data in terms of male versus female spiders? What do you predict about sex ratio given that you did this project in the autumn? I’d love to hear your thoughts about this!

    • We didn’t differentiate female and male spiders, because this often requires a deep knowledge of each species. However, some good old tricks work too, for example the male are often really small compare to female and possess larger pedipalps. So in this way, we can say that we generally found way more female spiders.
      Well, an educated hypothesis would be that female lay their eggs in the autumn, so they must be alive and more abundant. Males are discard (or eaten) right after they mated with a female. Also, since females carry the progeny and are often stronger they survive longer the temperature changes or other challenges of Nature.

  2. Nice! I wonder, will you further analyse the results with respect to the distances from the forest?
    I wish we had done such an awesome project in my undergrad! BTW, the spiders in the lower left picture appear to be philodromids of the genus Tibellus.

    • Yes we will. We are finding some interesting things, for example we found more spiders in the middle (line b) as we expected to find more in the forest edge.
      It is an amazing opportunity to do this field course. Thanks McGill !
      Nice, thanks for the tip!

  3. Please feel free to leave comments. We appreciate feedback.

  4. […] Undergraduate students in my field biology class wrote a blog post about spiders.  […]

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