The spider on the flower

The flower crab spider

The flower crab spider is an ambush hunter. It sits on a flower and takes on the petal colour. It waits for a bee or a butterfly to land within reach. The female can change colour from white to yellow and back. The change takes several days. The change works so well that a spider on a white daisy is almost unseen.

She builds no web to catch food. She hides by her colour and waits still. Then she strikes very fast. She can beat insects far larger than herself. The male is a small part of her size. He is a dark little spider that roams to find mates.

The species lives across Europe, Asia and North America. It is found in gardens, meadows and hedgerows. It stays out on flowers in daylight, so it is easy to watch. Its bite does no harm to people.

Family tree

A crab spider that spins no snare

The flower crab spider is in the order Araneae. Its family is Thomisidae. Its genus is Misumena. It is the only member of its genus across much of Europe. Its best-known kin in that order is the Yellow Garden Spider.

That is a large black-and-yellow orb weaver. It spins a big round web and waits for insects. The two spiders solve the same problem in opposite ways. The web spider uses silk. The crab spider uses colour and speed.

Crab spiders hold the front two pairs of legs wide, like a crab’s claws. The family Thomisidae has more than 2,000 species. It includes bird-dropping spiders. Misumena vatia is one of the few crab spiders that change colour. The species was named in 1775 by the Swedish naturalist Carl Clerck.

Colour, size and wide legs

How to identify one

An adult female is six to eleven millimetres long. The male is only three to four millimetres. The gap in size between the sexes is huge even for spiders. The female body is broad and flat. It has a rounded rear wide at the back. Her front two leg pairs are longer and thicker than the rear pairs. She holds them wide when she hunts. The female colour runs from pure white to bright lemon yellow.

Some are pink or green. Her rear body often shows faint dark stripes or spots. These show most on yellow ones. The male is darker. He has dark brown or black marks on a pale ground. He has a slim body and long legs. The eyes are small and set in two rows. Her sight is poor.

Yet she feels movement on the flower with great skill. She changes colour by moving colour grains in her outer skin. The move takes several days each way. A spider in mid-change may look pale yellow or creamy. Females shed their skin several times before full growth. They stop changing colour once grown. Both sexes can go without food for a long time while they wait.

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Sunny flowers everywhere

Where it hunts

The flower crab spider lives across Europe, Asia and North America. It ranges from lowland gardens and farms up to mountain meadows. It is absent only from the coldest and driest lands. It lives in any open, sunny spot with many flowers. Such spots are flower-rich grass, hedgerows, road sides, woodland paths, coastal dunes, waste land and gardens. It is often common in old meadows where insect numbers are high. Females spend most of their adult life on one flower head.

They like a broad flat surface. Good ones are a daisy, an ox-eye daisy, a buttercup, a knapweed, a thistle or a white umbel flower. They move only when the flower stops drawing insects. The spider takes the petal colour. Those on yellow flowers are yellow. Those on white flowers are white. Males are smaller and roam over plants.

They are often on leaves. The species peaks in June and July. That is when flowers bring bees and hoverflies. In southern Europe it may have more than one brood a year. Where meadows were re-sown or ploughed, the spider has faded. Old grassland and rough road sides are now its safe places.

What it eats

Sitting still and waiting

The flower crab spider eats the insects that visit flowers. Its food is mostly bees, hoverflies, butterflies, moths and other nectar seekers. It sits and takes what lands within reach. A large female can kill a honey bee, a bumblebee or a small butterfly many times her weight. The strike is very fast. She leaps and grabs the insect with her long front legs. She bites the back of the head or neck.

Venom stops the prey within seconds. Once beaten, it is held and eaten through the chelicerae. A big meal feeds her for several days. She does not use silk to catch prey. She lays a thread while moving. She uses silk to wrap the egg sac. Males are much smaller.

They take only flies and small hoverflies on leaves. In turn, crab spiders are eaten by birds, lizards, big wasps, ants and other spiders. Sitting out by day makes them easy prey. The female drops on a silk thread if disturbed. Her colour is her main guard.

Silk, eggs and a guarded mate

Courtship and young

Males grow up before the females. They roam to find mates using scent. When a male finds a female he comes close with care. He ties her with a thread of silk before mating. A hungry female would else treat him as food. After mating, the female keeps hunting and grows. Only later does she lay eggs. She lays them in a flat white egg sac.

It holds a few dozen to about two hundred eggs. She puts the sac in a folded leaf, a flower head or a curled stem. She spins a silk cover. She stays with it and guards it without eating. By the time the eggs hatch she is near death. In most groups she dies before winter. She leaves the sac to live through the cold. The young hatch in late summer or autumn.

They stay in the silk case a short while. Then they spread to find their own flowers. They spend the winter hidden in plants. They grow up the next spring or early summer. Males and females grow at slightly different times. Late females may not breed until the next year.

A sign of flower-rich land

Why it is becoming rarer

The flower crab spider has no set conservation rank. It is not protected. Yet it is a good sign of flower-rich land. It depends on flowers and the insects that visit them. So it is hurt by the same changes that cut bee, butterfly and hoverfly numbers across Europe. These are more intense farming, grass re-sowing and fertiliser use, loss of hedgerows and field edges, and heavy bug sprays.

Spraying a field or road side in summer takes females with their prey. Cutting verges and meadows again and again does the same. In Britain and northern Europe the species stays common where wildflower meadows survive. It does well in gardens and on waste land. No special plan exists. Care means keeping and bringing back flower-rich grass.

It means using less bug spray. It means leaving rough edges uncut in summer. Records rely on naturalists who photo spiders on flowers. Sightings are still patchy.

Quick hits

Five things to remember

• The female can change colour from white to yellow and back, and the change takes several days over the move.
• A single fast strike lets her kill a honey bee or a bumblebee many times her own weight.
• The male is only three to four millimetres long, less than half the size of the female.
• She builds no web to catch food and hides by her colour on a flower.
• She guards her egg sac in a folded leaf until she dies, and she does not eat again.