Crab spiders -- sometimes called flower spiders because many sit on or inside flowers waiting for bugs to drop in -- are named for their crablike legs and ability to use them to walk sideways, forward or backward.
Crab spiders do have some silk, but they don't appear to use it much. Males might loosely wrap females in some webbing -- perhaps a defense against being eaten -- but crab spiders are ambushers, not catchers.
They have excellent eyesight (and should, with eight eyeballs keeping a lookout) and can both hide from birds and other predators and watch for bugs.
Crab spiders are small, usually less than 1 inch, but are capable of grabbing bugs much larger than themselves. In fact, they have a poison potent enough to immediately kill bees and butterflies. Some scientific research, in fact, suggests that insects learn to avoid flowers where crab spiders are hanging out.
But while their diet may cause some loss of pollination, the spiders themselves act as pollinators and do so much damage to bad bugs that they more than offset the occasional loss of a butterfly or honeybee.
Their bite, incidentally, isn't dangerous to humans.
Males are typically smaller and darker than females, which leads to perhaps the most interesting feature of crab spiders. Most females found in the Northwest -- North America has about 200 of the world's 2,000 or so species of crab spiders -- are tan, white or cream. Over a period of a few days, they can change colors to match the flower they choose for an ambush -- kind of a chameleon spider.
Crab spiders, in fact, spend so much time and energy changing their color that if one is taken from a flower and put into a flower of a different color, it will often leave and look for the right color rather than try to change again.
-- Bill Monroe
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