Tiny white spiders wandering through your home can be a disconcerting sight. However, these spiders, commonly called crab spiders, are harmless to humans and help control pests on houseplants both indoors and in the garden. Though their natural colour is white, crab spiders are able to change colour to match the type of flower in which they hunt for insects.
Crab spiders are small spiders that are easy to identify by their stout body shape and conspicuous front two pairs of legs; the legs point forward from the spider's body and resemble crab pincers. Crab spiders have a round abdomen and very small cephalothorax. The spiders are usually white when they are moving from one plant to another. It takes a crab spider several days to change their colour to match the flower they live in, according to the University of Kentucky.
Crab spiders are ambush predators and do not spin webs to capture prey. Instead, they sit on flowers and wait for prey such as bees and wasps to arrive on the flower to collect pollen. The spiders quickly ambush unsuspecting insects by using their long legs to grasp onto the insect while injecting a potent venom strong enough to paralyse large bees. Once the insect is incapacitated, the spider sucks the nutrients from its prey.
While crab spiders do not pose a threat to humans, they kill beneficial insects such as bees and wasps that help pollinate many plants in home gardens. Crab spiders are generally considered beneficial creatures to have around since they feed on garden pests -- such as spider mites, aphids and flies that damage garden plants -- more often than they kill beneficial insects, according to the University of Michigan.
Although white crab spiders can be a beneficial insect in home gardens, they can be unsettling to have on indoor plants. Crab spiders move slowly and are easy to remove from indoor plants. Place a sheet of paper near the plant and use a pen or pencil to chase the crab spider on to the paper. Once on the paper, quickly cover the spider with a small cup and transport it outdoors and release the spider on a flowering plant away from your home.
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- University of Kentucky Entomology; Crab Spiders; Blake Newton; January 20, 2011
- University of Wisconsin, Milwaukee; Bug of the Week: Crab Spiders
- University of Michigan; Kids' Inquiry of Diverse Species; Crab Spiders; 2011
- Henderson State University: Thomisidae -- Crab Spiders;
- University of Missouri; Crab Spiders; March 2003