What do you see in this photo? A bumble bee. A small brown spider. White flowers. Look closely: There’s a large crab spider front and center. If you have a garden, you may be familiar with the goldenrod crab spider (Misumena vatia), which is commonly seen on flowers from late spring through early fall on the North Coast. Female crab spiders like the well-camouflaged one pictured here can change color between white and yellow to better match their environment — in this case, mapleleaf checkerbloom flowers on which the spider waits to ambush prey. The color switch occurs through transfer or excretion of yellow pigment when the spider molts. Female crab spiders seem to be aware of the hue of their habitat, for if a meddlesome naturalist places one on a plant where she is more conspicuous, she will move to a flower where she is less noticeable.
Unlike most spiders, the crab spider doesn’t spin a web. Instead, she captures prey by waiting in or on a flower with her two front pairs of legs held open to grab insects such as flies and bees. The big, white female in the photo has just caught a pollen-dusted bumble bee by snapping her four front legs together like an old-fashioned spring trap. She’ll need to eat a lot because she is gravid (pregnant), which you can tell by the size of her egg-filled abdomen. She will continue guarding her flowery hunting territory until her spiderlings have hatched, after which she dies.
What about the small brown spider? Well, crab spiders are a great example of sexual dimorphism, in which the females and males of a species are markedly different in appearance (size and color, for example). The little spider on the female’s abdomen is an adult male crab spider. Like most male spiders, he has enlarged pedipalps (those two little “clubs” in front of his first pair of legs). His darker coloration allows him to blend into the background, a necessary attribute because he is more susceptible to predation, being constantly out and about searching for females to mate with. In contrast, the female rarely leaves her flowers. Unlike many invertebrates, female crab spiders don’t emit pheromones, specialized chemicals that let the male know that she is ready to mate. Instead, she attracts a male by leaving silk draglines near her flowers.
This particular male is not looking for a mate but maybe a meal. He is most likely hoping to share her catch, and her abdomen is a safe perch since she can’t reach him there. Yes, she is that hungry. Sexual cannibalism is not uncommon in the goldenrod crab spider. It contributes to species survival, since the female needs lots of calories and nutrients for her eggs.
I appreciate the crab spiders in my native plant garden, but if I find them on ornamental plants that are bumble bee magnets such as hummingbird mint (Agastache) and cat mint (Nepeta), I carefully move the spiders to native plant flowers. I hope this example from my garden makes you curious enough to view your own garden as a sort of natural history classroom available year round. Share with your neighbors what you learn.
Pete Haggard (he/him) and Jane Monroe (she/her) are the coauthors of Rewilding: Native Gardening for the Pacific Northwest and North Coast, available now from The Press at Cal Poly Humboldt and in local bookstores and nurseries.
This article appears in The Disappearing Registrants.