Crab Spider

Crab spiders make up the family Thomisidae, a diverse group of over 2,000 species found worldwide, named for their crab-like habit of holding their two long front pairs of legs out to the sides and sometimes walking sideways or backward. Rather than building webs, crab spiders rely on camouflage and ambush, and some species, such as the goldenrod crab spider, are even capable of slowly shifting their body color between white and yellow to match the flower they are hunting from.

Because they frequently hunt on flowers, crab spiders are a common sight for anyone who spends time watching garden blooms, often going unnoticed until a visiting bee or fly is suddenly seized. Other species in the family live on bark or leaf litter, relying on mottled coloration rather than bright hues to stay hidden.

As ambush predators of flower-visiting insects, crab spiders occupy an interesting ecological niche at the intersection of pollinator and predator communities, feeding on the very insects that flowers are trying to attract.

• Two front pairs of legs noticeably longer and heavier than the rear pairs, held out to the sides in a crab-like stance
• Broad, flattened abdomen, often wider than it is long
• Coloration highly variable by species: bright white, yellow, pink, or green in flower-dwelling species, and mottled brown or gray in bark-dwelling species
• Capable of walking sideways or backward, unlike most spiders
• Does not build a capture web; found sitting motionless on flowers, leaves, or bark
• Lookalikes include jumping spiders, which have a more compact body and much larger forward-facing eyes

Crab spiders are found on flowers, foliage, and bark in gardens, meadows, woodland edges, and shrubland across nearly every continent. Flower-dwelling species are most active during the blooming season when nectar and pollen draw in insect prey, while bark- and litter-dwelling species remain active on tree trunks and the forest floor throughout warmer months.

Crab spiders are sit-and-wait predators that rely almost entirely on camouflage rather than silk traps. A flower crab spider will often remain motionless on a bloom for hours or days, sometimes slowly adjusting its pigmentation to better match the petal color, until a bee, fly, or butterfly lands within reach. It then seizes the prey with its long front legs and delivers a quick bite to subdue it, often taking insects considerably larger than itself. Crab spiders are not aggressive toward anything they cannot overpower and will typically freeze or drop away if disturbed. Within their ecosystems, they help regulate populations of flower-visiting insects.

Females lay eggs in a flattened silk sac, often folded within a curled leaf, and guard it until the spiderlings hatch. The young disperse to find their own hunting perches, and some species produce silk draglines to balloon on air currents to new locations. Spiderlings molt several times over the course of a season, with most species completing one generation per year in temperate climates. In colder regions, spiders typically overwinter as eggs or as partially grown juveniles, resuming development the following spring.