Spiders are a diverse and amazing group of arthropods comprising the order Araneae. They are not insects. They often elicit strong reactions in people, but injurious spider bites are very rare.
This year, the Environmental Monitoring Program (EMP for short) of the Canadian Museum of Nature began to survey spiders on the 76 hectare property that comprises the museum’s research and collection campus in Gatineau, Quebec. Spiders have very diverse life styles: some dig tunnels, many use webs to catch prey, and some use their silk as a sail to get around. Some species even live under water!
The EMP students began collecting spiders in addition to continuing to collect beetles. The spiders were collected using the same pitfall traps that we use to collect ground beetles.
“Beating” is a second method of spider collecting that we tried out this season. This technique involves holding a sheet beneath a tree and shaking the tree vigorously. Any spiders that fall onto the sheet need to be sucked up quickly using an aspirator. This requires a lot more time and energy than the passive pitfall traps.
There is evidence that spider assemblages change as the environment around them changes. A change in the spider species that are present is reflective of an environmental change in our forest.
Once collected, we preserved our specimens in ethanol and brought them back to the lab for sorting. When trying to identify spider families, there are a few key features that are used. Often, eye arrangement indicates the appropriate family, such as the wolf spider family (Lycosidae), which has four large posterior eyes that form a rectangle if you look from the top, and four much smaller anterior eyes that form a row in front.
The crab spider family is easy to recognize by body shape with its longer first and second that resemble those of a crab. Other families can be much trickier to identify, requiring us to count the number of large hairs (macrosetae) on a segment of a specific leg.
To identify spiders to species, we would need to look more closely at their genitalia because these structures are very species-specific.
Before mating, males create a web where they deposit their sperm. They then collect the sperm in their secondary genitalia and store it near their head in specialized structures. Called pedipalps, they resemble ornate glasswork or sugar-work and are inserted into the female’s epigynum during mating. The spiders’ genital structures function like a lock-and-key mechanism.
After mating, some males leave in a hurry, leaving a palp behind. This effectively blocks any other males from mating with the female.
There are over 100 families and 35 000 species of spiders in the world. When you take a closer look under a microscope, you can see how different these species really are.
Spiders may never win everyone’s approval, but now EMP students react with excitement, curiosity and appreciation when they see spiders.