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Right In Your Own Backyard

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Published on: Jul. 2, 2001

Last revision: Nov. 9, 2010

Look closely at the flowers in your backyard and you may see tiny hunters that sit on or creep around on the flowers and capture other small animals. Their world is small but, in it, flower spiders are just as ferocious as lions, tigers or bears.

Flower spiders look and move a lot like crabs, which is why many people call them crab spiders. They are short and broad and have two pairs of long front legs that they hold out like crab claws. Furthermore, they seem to prefer moving sideways and backward rather than forward.

Flower spiders eat insects and other spiders. Unlike many spiders, they do not spin webs. Instead, they ambush their prey. They use their long, pincer-like legs to guide their victims into their powerful jaws. Once in the grasp of the jaws, the prey has virtually no chance of escape. With its jaws, the spider injects venom that liquefies its victim's organs, and then it sucks its victim dry.

Females, which are seldom longer than 10 millimeters, spend their lives on flowers. Males are about half the size of females and spend most of their lives searching for food on the ground. They generally appear on flowers only for mating.

Female flower spiders sit motionless on flower heads waiting to grab insects that come to gather nectar and pollen. They seem to prefer ray-type flowers. If they can successfully feed, they may remain on the same flower for several days or on the same plant for several weeks, but they will quickly abandon flowers that do not attract sufficient numbers of insects.

When disturbed, flower spiders move below the flower, returning to the top when danger has passed. While photographing them, I think I bothered some flower spiders so much with my electronic flash that they wrapped themselves in petals so they could remain atop the flower within reach of visiting insects. I have not observed this behavior at any other time.

In contrast to other spiders, female flower spiders can change color to a limited degree. This allows them to remain hidden on different parts of a flower or on different colored flowers. They may take a few days to change color, and most change only between white and yellow. As expected, they often are found on white and yellow ray flowers, such as oxeye daisies and black-eyed Susans, which draw a variety of insects. Some may develop other colors as well, such as orange and pink. More than 80 percent of flower spiders select flowers that match their body colors. Why the others do not is unknown.

Flower spiders often take insects much larger than themselves, such as large bees, wasps or butterflies. I often wondered what kept large insects from just flying off with the flower spiders in tow. One day, I discovered the reason. I was watching a flower spider when it grabbed a skipper (a type of butterfly) that lit on a black-eyed Susan. The skipper took flight but came to an abrupt halt as it reached the end of an anchor line of webbing the spider had attached to the flower. Both skipper and spider flopped over the edge of the flower. Swiftly, the spider reeled in the anchor line, pulling itself and its prey back up to the flower, where it consumed the skipper's body fluid.

Normally, flower spiders feed in the open atop the flowers, and they tend to hold their victims in a natural way that gives the appearance the insect is merely feeding or resting. Apparently, this fools birds and other potential predators that might eat the spiders. Predators are more likely to attack the more visible insect, allowing time for the less conspicuous spider to escape.

Wouldn't you like to see one of these amazing creatures? Go out in your backyard or a park and carefully look on top and under the flowers. Remember that flower spiders are very small. You can see them much better if you use a magnifying glass. You may have to look at many flowers to find them, and you will have better luck if you look where bug spray has not been used. Look for them in mid-summer and fall when the insects they eat are most common.

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