Flower Crab Spiders
And the Bees They Love
At the end of August, flora in our area changes dramatically – mid-summer flowers give way to the goldenrod, thistles, asters and Queen Anne's lace of late summer and early fall. With this change, many bees disappear. The colonies of various bumble bee species die off, and only their queens continue on, hibernating underground until spring.
The common eastern bumble bee (Bombus impatiens), however, braves its way through the end of fall, adapting to the succession of new autumn plants. This changeover requires a second set of skills – eluding the goldenrod crab spider (Misumena vatia), which lurks in late summer and fall on late-blooming flowers. This spider is joined by its cousin, the white-banded crab spider (Misumenoides formosipes).
Crab spiders get their common name from their tendency to hold their front legs aloft like crabs, and from their ability to run sideways as well as frontwards and backwards. The two species found in our area -- the goldenrod crab spider and the white-banded crab spider -- both belong to the family Thomisidae, commonly referred to as flower spiders.
Both goldenrod and white-banded crab spiders like to ensconce themselves within flowers, positioning their bodies to look like the bright yellow, pollen-bearing centers of blossoms. In the alternative, the spiders sometimes camouflage themselves to match a flower’s color.
This goldenrod crab spider has a singular skill. Naturally white, it can change to yellow when situated on a yellow flower like goldenrod. The spider’s body produces a yellow pigment that becomes more intensely colored the longer the spider remains on the yellow surface.
Later, if the goldenrod crab spider moves to a white flower, such as heath aster or Queen Anne's lace, it can excrete yellow pigment in order to turn white. These changes are produced by visual feedback: if the spider's eyes are covered, it cannot change color.
The transformation from yellow back to white takes about a week. A white goldenrod crab spider can then revert again to its yellow state – although to change back to yellow a second time requires much longer, because the goldenrod crab spider must produce a new store of yellow pigment first.
The white-banded crab spider undergoes similar transformations, although the mechanism of its color changes has been debated. Some sources theorize that the white-banded crab spider turns white or yellow according to the color of the flower on which it rests. Others hold that the hue of the flower on which the spider deposits its eggs determines the color of its progeny.
Although these spiders show a strong preference for yellow and white flowers, they are also commonly found on purple thistles and asters and plants of other hues. The spiders sometimes display themselves in isolation, in a flower-like stance, stretching their legs outward to mimic flower petals -- this behavior is another means of luring in prey.
Whether by masquerading as a flower or a yellow flower-center, goldenrod and white-banded crab spiders kill by ambush. They wait for an unsuspecting bee to stroll too close and then, in one quick motion, the spiders extend their long legs and wrap them around the bee. The spiders sink their fangs into their prey, injecting it with venom.
The weaponry of crab spiders is typical of many spiders – a pair of jaws with leglike joints, called a chelicerae. Each jaw is made up of a sharp retracted fang housed in a casing known as the basal segment. The fang is hollow, with a duct at the bottom that connects to the spider’s venom gland. When the spider springs, it squeezes out the venom in a plunger-action, like a hypodermic syringe.
The venom of goldenrod and white-banded crab spiders is a neurotoxin that paralyzes the unsuspecting pollinator. (You might like knowing that spiders have possessed the capacity to kill with poison for hundreds of millions of years, far, far longer than humans have been or will be on earth.) Harmless to humans, the crab spider’s neurotoxin is extremely poisonous to bees. The paralyzing agents of the crab spider's venom allow it to immobilize its prey, so that the spider can eat in peace.
As you might expect from a killer who kills by ambush, these spiders are relatively shy: if you try to photograph them with a macro lens, goldenrod and white-banded crab spiders often will scamper to the far side of whatever stem or flower they have climbed onto, much like a squirrel that evades capture by running to the back of a tree and circling it as you move around the tree. These spiders also like to hide by grabbing the edges of flower petals and folding them over their bodies.
If you disturb a crab spider when it already has captured its prey, the spider is likely to drag its captive a considerable distance to elude your prying eyes. Goldenrod and white-banded crab spiders are disproportionately strong. The spider at top right, for example, hauled a common eastern bumble bee several times its size up and down a thistle stalk without once letting go.
During the fall, local goldenrod-filled meadows are littered with the bodies of common eastern bumble bees. In fact, if you see a dead bumble bee on a goldenrod plant, it's worth leaning down and looking under the bee to see if a crab spider is connected to it via two fangs.
Goldenrod and white-banded crab spiders, however, do not merely capture bumble bees. They feed on almost anything that comes their way -- including honey bees, butterflies, dragonflies, nocturnal moths, yellow jackets, flies -- and even spiders. Mature female bees are lbig enough to take down even large insects. Males are much smaller than females and eat smaller prey; during mating season, males also may drink flower nectar.
Because goldenrod crab spiders live by ambush, they do not make webs and do not wrap their prey in silk. Goldenrod and white-banded crab spiders can, however, produce a dragline -- a single thread that allows them to drop quickly to the ground to avoid predators (and photographers). The spider can then climb back up the dragline to resume its position on a flower and to await its next ambush.
Both goldenrod and white-banded crab spiders reach maturity in late summer or fall. After mating, females spin egg sacs, deposit eggs in them and stand guard over them unto their deaths at the beginning of winter. Spiderlings hatch within a month after eggs are laid and overwinter in the egg sacs.
Goldenrod crab spiders (Misumena vatia) and white-banded crab spiders (Misumenoides formosipes) are the two principal crab spider species of New York State. Because females of both species tends to appear in both white and yellow, they can be tricky to distinguish from each other.
The genus names of both spiders derive from misumens, Greek for "object of hate". Formosipes comes from the Latin for "beautiful foot". These oddly-paired words evoke the essence of the white-banded crab spider, at once a fascinating object of delicate beauty and a source of terror.
"Vatia," on the other hand, means "bow-legged". Thus, both bees' scientific names focus attention on the spiders' most salient characteristic -- their long, curved, tapered front legs. In both species, the front two pairs of the spider's legs are longer than its hind pairs, a trait common to members of the family Thomisidae.
Females of the two spiders species are best told apart by the appearance and positioning of their eight eyes. On goldenrod crab spiders, all eight eyes are visible from the front and grouped in a crescent shape.
On white-banded spiders, the outermost pair of hind eyes is difficult to see from the front; the two eyes point outward, set near the ends of a long horizontal ridge that runs across the spider's face. (These differences are shown in the photo strip at right.) These spiders are, accordingly, sometimes called "ridge-faced flower spiders".
Female goldenrod crab spiders sometimes sport red markings, like the spider shown above right. Such markings are suggestive of the adornments found on flowers and enhance the spider's efforts to masquerade as a flower. These markings result from the individual spider's genetic makeup, and do not change color when the spider does.
Female white-banded crab spiders sometimes appear light brown, rather than yellow or white. Their abdomens usually have a V-shaped design made up of spots or stripes, and may have red, brown or black markings. The female spider's cephalothorax can be green, brownish or reddish.
Both goldenrod and white-banded crab spider males lack the ability to change color by producing and excreting yellow pigment. (Juvenile goldenrod crab spiders may change color according to what they eat, but they lack the ability to produce yellow pigment.)
Male goldenrod crab spiders have yellow or off-white abdomens divided by two reddish-brown bands or broken dashes. The males' cephalothoraxes are dark red or brown, with a light band down the center. Male white-banded crab spiders have red or yellow abdomens; their carapaces can be orange, red, or green.
Female goldenrod crab spiders run from 1/4" to a little more than 1/3" (body length only). Males are between 1/10" and 1/6". Female white-banded flower spiders tend to be between 1/4" and 1/2". Males are around 1/8".
A white-banded crab spider carries a large common eastern bumble bee along a thistle stem.
A white-banded crab spider masquerading as a flower's yellow center nabs a common eastern bumble bee.
A female goldenrod crab spider with white coloration and red markings.
A female white-banded crab spider with white coloration, on a purple thistle.
PHOTO CREDITS: All photos and text © Copyright 2014-2017 Paula Sharp and Ross Eatman, unless otherwise noted. All rights reserved. If you wish to use any of the photographs here for educational or other purposes, please read permissions page.
REFERENCES: For a comprehensive list of references used in compiling this guide, click here: