In the past, we’ve had a number of these curious, chameleonic crab spiders show up in our balcony garden of four terrariums overflowing with plants. This week I found a red-marked female of the genus Mecaphesa on a yellow thistle bloom. There are about 16 species of Mecaphesa in California. The only way to determine the species for sure, according to the experts, is by “a close examination of the spider’s reproductive structures and setal pattern.” Setae are the sensory hairs on the legs and body — in Mecaphesa they are quite long and easy to see.
This female waited patiently on a yellow thistle bloom.
The long, sensory hairs called setae are visible on the spider’s legs. Crab spiders have very long front legs for capturing their prey.
Steven E. F. Brown 