Tay Meadows Tidbit – Pseudoscorpion

Pseudoscorpion, Chelifer cancroides

When I went to brush my teeth last night, I noticed this guy hiding behind the faucet. I put down my toothbrush and hurried to grab my camera and macro lens instead. The macro because it’s tiny, perhaps just half a centimetre (less than 1/4″). He was pretty obliging about hanging out for some photos, and the white porcelain sink made a nice, uncluttered background.

The critter is a pseudoscorpion. As you might guess by the number of legs on the body, pseudoscorpions are relatives of spiders, also found in Class Arachnida. Like spiders, they produce venom and silk, although the venom is injected through the pincer, and the silk is produced by a gland in their jaws rather than on their abdomen. Although they look just like scorpions without a tail, the similarity is superficial, as scorpions belong to a different Order (Scorpiones instead of Pseudoscorpionida).

Pseudoscorpion, Chelifer cancroides

There are some 3300 species of pseudoscorpion around the world, with potentially upward of 350 species in North America north of Mexico. Most of the diversity occurs farther south; up here there are probably fewer than 50 species that occur in Canada. They are found in virtually every habitat, from the deserts of the southwest to the northern taiga and tundra. There is one species that is so closely tied to human settlement that its habitat is described as “Houses, building, barns”, and is “often found crawling on the walls of older homes, particularly in humid locations”. That species would be Chelifer cancroides, and is the species that I believe my pseudoscorpion to most likely be, although apparently being able to definitively tell the difference between it and another Chelifer species requires being able to count the setae (hairs) on the pincer and examine the venom gland.

Pseudoscorpion, Chelifer cancroides
Also superficially resembles a crab, except crabs have tails that curl underneath their abdomens. No tail on this guy. (This is his underside. I flipped him gently with a Q-tip for this photo.)

When prodded, the pseudoscorpion goes into a defensive posture, pulling its pincers back toward its body. Its pincers aren’t limbs in the traditional sense, but are actually modified palps, mouthparts, much the way male spiders have swollen “mitts” in front of their faces. They use the palps primarily for hunting, stinging and immobilizing the prey with the venom gland located on the thumb-like inner pincer (the outer one is fixed). They apparently do not ingest the prey whole, but rather secrete digestive enzymes onto the prey and then “suck up” the liquified remains (this isn’t that different from the dietary habits of a spider, except the spider usually wraps its prey up with silk, first). Pseudoscorpions prey on dust mites and book lice, so are good to have around the home. Once it reaches maturity, an individual may live as long as two to three years.