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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.
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.
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).
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).
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).
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 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:
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.
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.
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.
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