You must be watching a goldenrod crab spider, Misumena vatia, of the family Thomisidae. It is featured in the book, "Predator upon a Flower: Life History and Fitness in a Crab Spider," by Douglass H. Morse (take a look at the front cover to confirm your spider's identity). Crab spiders are considered beneficial to humans. Although they eat a few bees and wasps, they also kill flies, mosquitoes, moths, and other insect pests. Crab spiders are masters of ambush and disguise. The goldenrod crab spider is a free-living spider that resembles a small fiddler crab. It makes use of the camouflage techniques and catches its prey with its front clawlike legs. The first and second pairs of legs are noticeably longer and thicker than the last two pairs. They have a squat flat body. The round abdomen shows small dimples and there is a red stripe on the side. These spiders are able to change their color over several days, typically between white and yellow, depending on the color of the flower on which they are resting. The change between white and yellow takes a couple of days to complete. Crab spiders are easily recognizable if you tease them. They widen their legs and move sideways like a crab. Crab spiders are often noticed only when one sees a strangely positioned upside-down insect in the grips of a spider. Goldenrod crab spiders do not spin webs to trap prey, but they hunt on flowers. Often the crab spider remains for days, even weeks, at the same spot. Typical goldenrod crabs are found with front legs extended inside or concealed just beneath a flower ready to ambush their prey. A suitable prey insect can be up to three times her size. When the prey lands on a flower, the spider swiftly grabs it and pierces it with small fangs behind the head. Paralyzing venom keeps the prey immobilized with its heart pumping. The insides are dissolved and sucked from the exoskeleton, and the empty, perfect form of the insect is dropped to the ground. The female crab spider is considerably larger than her mate. Females are about 5/16-inch and males are only 1/8-inch long. Often a small male can be seen riding piggyback on the female. The male seeks out a subadult female and waits for her final molt. During the final molt she is incapable of resisting his advances or attacking him. He makes his move and mates. He then leaves to find another defenseless female crab spider. The females probably attract the males with pheromones. After mating, she lays her eggs in a leaf curled much like an ice cream cone. She actively guards her egg sac without eating, but dies before the young spiderlings hatch. Crab spiders go through a simple metamorphosis. Young goldenrod crab spiders hatch from eggs and look like tiny adults. The color of the young will resemble the vegetation rather than their parent. They shed their skin as they grow. Most crab spiders live for less than one year and have only one generation per year. In most of these species, the females produce eggs in the fall, and the offspring hatch in the spring.

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