Bug of the Week

Crab Spiders (Family Thomisidae)


Howdy, BugFans,

This stars of this week’s episode are not insects, but crab spiders, one of the Bug Lady’s favorite critters. They fit into the phylum Arthropoda (“jointed legs”) which consists of the Crustaceans, the Insects and the Arachnids, are in the Class Arachnida and are true spiders in the Order Araneae. (In other words, Arachnids are under the big Arthropod “umbrella,” which shelters, among others, shrimp, crabs, sowbugs, scorpions, spiders/spider relative/mites/ticks, millipedes, centipedes and insects. Araneae or true spiders are, in turn, under the Arachnid umbrella). They have 2 body segments, a cephalothorax and an abdomen, and 8 legs. Crab spiders are so named because they sidle across the flower tops with their front legs held like crab claws. There are about 200 species in the North America. Crab spiders don’t make webs.

A not-so-camouflaged but still successful crab spider. Male crab spiders look surprisingly different from the females.
A not-so-camouflaged but still successful crab spider. Male crab spiders look surprisingly different from the females.

The flower spider or goldenrod spider (Misumena vatia) is a common species. These come in white and yellow models with the red racing stripes that explain their other name – Red-spotted Crab spider. They can change color from one to the other in about 10 days, so you frequently see white spiders on white flowers and yellow on yellow (but they don’t turn purple or rose).

Crab spiders will tackle prey that’s larger than they are. The BugLady enjoys looking for pint-sized crab spiders as she walks.
Crab spiders will tackle prey that’s larger than they are. The BugLady enjoys looking for pint-sized crab spiders as she walks.

It looks like the male crab spider on the Black-eyed Susan was about to have a “gottcha” moment until the BugLady’s camera interrupted. According to the small but excellent Golden Guide to Spiders and their kin, “They have good eyesight, and when they nab their prey, they hold it up in the air and suck out the juices.”

'Nesting' crab spiders undefined
'Nesting' crab spiders. Another 'nesting' crab spider.

The Nesting” crab spiders remind the BugLady of those Russian matrushka nesting doll sets. The BugLady has been brainstorming with herself about what is going on here. A spider is shedding its skin? They generally pull themselves out through a split in the abdomen, not through the mouth. A (blush) post-mating bit of cannibalism? The “eatee” looks like the same gender as the “eater.” Simple predation (again, cannibalism)? Tough room!

The Bug Lady