When I was out picking raspberries the other day the other day, I found a pretty little white spider waving its long front legs at me.
Getting closer, I see that this is a crab spider, an ambush predator that sits and waits for prey to come near and then reaches out to snare them with its long front legs.
I’m intrigued by the strawberry colored marking on the sides of this little spider, which should make it easy to identify.
Usually, these flower crab spiders are well camouflaged by matching the color of the flower, yellow or white, on which they are sitting. The white-flowered raspberries have finished blooming, however, so this crab spider stands out against green leaves and red fruit. Time for it to move to the back yard and start hunting on the yellow oxeye, black-eyed susans, and yellow coneflowers.
In its yellow form, the crab spider blends perfectly with its background on the flower, but how does a white spider turn yellow? By secreting yellow pigment from the top layer of cells in its outer covering into the white, pigment-containing cells below, flower crab spiders can be chameleon-like, changing gradually over a period of 10-20 days from white to yellow. Yellow spiders that move to white flowers excrete their yellow pigment and transform into white spiders in a mere 6 days.
Visual input is highly important in stimulating and achieving the spider’s color matching to its background; spiders whose “eyes” were painted over lost the ability to change color.
Apparently, only the females are the chameleons of this species; males which are a small fraction of the size of the females, are yellow-brown and cannot change color.