The Spider Sitting on a Flower

Crab spiders do not build webs. They choose a flower and wait, sometimes for days.

Recognising them

Held like a crab. The two front pairs of legs are longer and heavier than the back two and are held out to the sides, which produces a distinctly crab-like posture and gives the family its name.

Sideways movement. They walk sideways and backwards readily, again like a crab.

No web. There is silk — a dragline and an egg sac — and no capture web at all.

Squat and flattened, with a wide abdomen.

The colour change

The goldenrod crab spider is the well-known one. It can shift between white and yellow by secreting a yellow pigment into the outer cells or reabsorbing it.

The change takes days in one direction and longer in the other, which means the spider commits to a flower colour rather than adjusting on arrival. A yellow individual on a white daisy is one that has moved recently.

What they catch

Prey much larger than themselves. A crab spider on a flower takes honeybees, bumblebees, butterflies and hoverflies, holding them with those heavy front legs while a fast-acting venom takes effect.

That is why they sit on flowers: the flower does the attracting, and the spider only has to wait.

Green lynx spiders

Frequently found alongside and often confused with them. Bright green, spiny legs, and a habit of sitting on flower heads in the southern United States.

Lynx spiders are more active than crab spiders — they chase and leap rather than waiting — and their legs carry conspicuous black spines that crab spiders lack.

Are they harmful

No. They are small, reluctant to bite, and their venom is adapted to insects. Handling one produces nothing worse than a hurried retreat.

The green lynx is occasionally reported as spitting venom when its egg sac is threatened, which it can do over a short distance, and it is an irritant rather than a hazard.

In the garden

Crab spiders are predators of pollinators, which makes them an awkward presence for anyone growing for bees.

The scale is small. A garden supports a few crab spiders and thousands of pollinator visits, and the spiders are themselves prey for birds and wasps. Removing them changes very little and removes an interesting animal.

Finding them

They are hard to see, which is the point of the camouflage. The reliable method is to look for a flower that seems to have a bee stuck to it at an odd angle — the prey is far easier to spot than the spider holding it.

Once found, they are excellent subjects for a photograph, since they are motionless by profession and will tolerate a lens at close range.

Other ambush hunters nearby

Jumping spiders share the same flowers and hunt entirely differently — actively stalking rather than waiting, and watching whatever moves nearby, as jumping spiders describes.

Orb weavers occupy the space between plants rather than the flowers themselves, and their webs catch what the crab spiders miss, which is covered in orb weavers in the garden.

Indoors

Crab spiders do not live in houses. One found indoors has come in on cut flowers or on clothing and will not establish.

Putting it back outside on a flowering plant is the whole intervention, and the technique in getting spiders out alive is more than adequate for an animal this slow.