Goldenrod Crab Spider

Misumena vatia — the goldenrod crab spider — is one of the most extraordinary CHAMELEON-LIKE color-changing arthropods in North America and one of about 2,150 species in family Thomisidae (the crab spiders — named for the sideways-walking gait that resembles crab locomotion). The species is widespread across all of North America, Europe, and northern Asia (Holarctic distribution). Females are 6-10 mm body length (males much smaller, 3-4 mm), with the species' two front pairs of legs much longer than the rear two pairs (the diagnostic crab-spider body plan). The species is famous for one of the most extraordinary examples of DYNAMIC COLOR CHANGE in arthropod biology. Female goldenrod crab spiders can REVERSIBLY CHANGE BODY COLOR between WHITE and BRIGHT YELLOW depending on the flower color they are sitting on — white flowers (daisies, white asters) trigger the spider to develop white coloration; yellow flowers (goldenrod, sunflowers) trigger yellow coloration. The color change is mediated by liquid pigment within transparent epidermal cells in the spider's exoskeleton — yellow color is produced by yellow pigment circulated through the cells, white color by lack of pigment. The transition takes 10-25 DAYS in either direction (much slower than the rapid color changes of cephalopods or chameleons), and the spider tracks flower color over several days of consecutive perching on a single flower or flower-color group. The color change matches the spider's body color to the flower color, providing CAMOUFLAGE against both PREY INSECTS (bees, butterflies, flies that visit the flower for nectar are less likely to detect the camouflaged spider before being seized) and BIRD PREDATORS (the cryptic spider is harder to spot against a flower than an exposed spider would be). The species also exhibits the diagnostic CRAB-SPIDER BEHAVIOR: walking sideways like a crab (the spider can move forward, backward, or sideways with equal facility, but typically moves sideways when on flower petals). Goldenrod crab spiders sit motionless on flower petals (often with the front legs raised in an ambush posture) waiting for pollinating insects to land on the flower, then seize the prey with the long front legs and inject venom from the chelicerae. Despite the small size, crab spiders can capture prey much larger than themselves (including large bumblebees and butterflies — the venom is fast-acting and the prey is paralyzed before it can sting or escape). Females eat very heavily on captured prey, building reserves for egg-laying; males do not feed once mature and live only long enough to mate. The species is harmless to humans (no medically-significant venom) and is one of the most-photographed crab spiders in NA macro nature photography because of the dramatic color change biology.