What scuttles sideways and backward, has long front legs held outward in a menacing way and a flattened body, and does not live on a beach? If you guessed crab spider, you are a natural observer.
Rather than building webs or making holes in the ground to catch prey, the crab spider family practices ambush hunting. Crab spiders sit on blooming flowers or on forest leaf litter with their two front pair of legs held out to the side (like a crab), ready to seize unsuspecting insects. Because of their good eyesight, they are able to quickly grasp prey much bigger than themselves, holding on only with their jaws.
Spiders can only eat liquids, so crab spiders inject venom from their fangs to subdue prey and then insert enzymes to soften the victim’s insides. Powerful stomach muscles make it possible for crab spiders to suck up their meal.
Did you know crab spiders can change color? The female goldenrod crab spider, for example, normally is yellow with two pink wavy lines on the sides of a round abdomen. The eye pattern forms a triangle tinged with red. Its carapace and legs are also yellow. To camouflage itself on a white flower, it changes to white after several days but retains the pinkish marks. The goldenrod crab spider often visits blooming field flowers, such as black-eyed Susan, dandelion, coreopsis, and goldenrod. White spiders can be found on Queen Anne’s lace or oxeye daisy flowers and turn pale green when moving onto green flowers.
Male and female crab spiders are sexually dimorphic, exhibiting different traits based on sex. Colored differently than females, males have a pale brown abdomen with two dark lines and a dark reddish-brown carapace that shows off a lighter median line extending from the eyes. They are also about one-third to one-half the size of females.
After maturing in early summer, male and female spiders come together only to mate. A female spider wraps her eggs in silk and attaches the egg sac to a folded leaf, closing it with more silk. Six spinnerets inside the posterior end of the abdomen produce the liquid silk, which quickly solidifies when forced out and exposed to air. The female guards the egg sac until she dies, which is sometimes before her young hatch. The spiderlings overwinter in hidden locations under logs or layers of leaf litter.
Don’t Be Scared of This Spider
There are 130 species in the crab spider family Thomasidae throughout North America. They are not known to be harmful to humans, and they do not enter homes.
The transverse-banded crab spider is another common species. It has a tan body, dark brown lines on the carapace, and dark brown splotches on a round abdomen. This is a tiny spider: Males are between 3mm and 7mm long, and females range from 4mm to 9mm. This species hunts through woodland leaf litter or among grass in meadows.
The northern crab spider is identified by a yellow body and legs, two reddish lateral lines on the carapace, and pinkish streaks and splotches on the abdomen. It changes colors and can be found on daisies, sunflowers, or the green leaves of iris.
Predators such as crab spiders are just as important to a natural garden as pollinators. In food webs, spiders comprise almost half the diet of many songbirds, including wrens and thrushes, and help to keep herbivores in check. Mud dauber wasps catch and paralyze spiders, place them in mud tube nests, and lay eggs on them, creating a food source for wasp larvae.