MARBLED SPIDER - Araneus marmoreus
If I were to write the story of Missouri spiders in the style of a murder-mystery novel, it might be a best seller. Picture a dark, eerie cellar or forest. The damsel spider lures her gentleman friend into her parlor-web and the promptly murders him with sharp fangs. This is the way of some spiders, minus the anthropomorphic tone, while other spider matings last a long time. Among the more than 35,000 species of spiders worldwide, each has its own peculiar story.
In the United States, we seem to see spiders as villains and take pains to avoid them. Only a few folk-beliefs show traces of regard or respect. As a child, I learned that it was unlucky to step on a crack or a spider. A college roommate of mine kept a tiny jumping spider in a small glass box because her family did so to bring their home good luck. "I don't ever kill a spider," an elderly ozark man once said to me, "because my grand daddy told me it'll rain for weeks on end if you do."
Despite our squeamishness about them, spiders do not hold a loathsome reputation universally. In some parts of the world, people believe that giving a spider as a gift or meeting a spider will bring good fortune, a successful marriage, fair weather or raise the ghost of your grandparent.
A spider is not an insect. It has eight legs, no visible antennae and a two-piece body. Spiders, along with tics, mites, harvestmen and scorpions, belong to the class arachnida. A spider has silk-spinning structures, called spinnerets, at the back end of its abdomen, and usually eight eyes of various sizes and shapes grace its face.
A spider's mouth parts, too, are different from an insect's. Instead of mandibles capable of chewing, spiders have fang-tipped jaws called chelicerae. With these, they pierce their prey and inject a toxic fluid that immobilizes it; digestive juices dissolve its internal tissues. The spider's small, tubelike mouth, aided by strong abdominal muscles, pumps and sucks the victim until it is a shriveled husk. A strong-jawed spider, like the yellow garden spider or the tarantula, often mashes its prey between its chelicerae while ejecting digestive juices over it.
Missouri is home to more than 300 species of spiders. Some individuals are the size of a pinhead and are easily overlooked. Others are surprisingly large, with a legspan of 4 or more inches. Size is helpful when determining the two suborders of spiders, though other characteristics are more diagnostic. The orthognatha, which includes the tarantulas and trapdoor spiders, are generally large, with stout bodies, stout legs, and jaws that move vertically. They also tend to be long-lived, some up to 25 years. The labidognatha, which includes garden spiders and orbweavers, generally have thinner bodies, spindly legs, and have jaws that move horizontally. The majority of spiders in Missouri belong to this suborder.
Spiders live in virtually every type of habitat in Missouri-and in staggering numbers. British arachnologists have estimated populations ranging from 11,000 spiders per acre in woodlands to more than 2 1/2 million individuals in a grassland acre.
On agricultural lands, spiders are a boon, destroying huge numbers of crop-damaging insects. Since each spider in a field may consume a least one insect per day, their cumulative effect on insect populations is significant.
All spiders are potential predators on many arthropods, especially the insects. Most prey upon grasshoppers, flies, moths, caterpillars, leafhoppers, some bees and ants, and other spiders.
The worst enemies of spiders usually are other spiders, but some insects, like the assassin bug and mud dauber wasp, prey upon them, as do bats, shrews and birds. Some orb weaving spiders construct a zig-zag pattern of silk, the stabilimentum, at the hub of their webs which, scientists hypothesize, may deter birds from flying into the silk structure. But it might also help birds locate an orb weaver in order to prey upon it.
With a few exceptions, Missouri spiders rarely live longer than a year. Some hibernate in winter under tree bark or rocks, or in cellars and attics, but many die within one warm season, leaving the future to an over-wintering brood of encased eggs. Spiderlings emerge in spring and summer from egg sacs suspended from vegetation or from flattened silk sacs constructed on leaves or in flower heads. Some spiders leave egg sacs in burrows under rocks, while others, such as wolf spider, carry the nursery with them.
Young spiders travel by climbing to the tops of grass blades, fenceposts or shrubs, elevating their abdomens and throwing out silken threads. Caught by the air currents, the tiny arachnids appear to fly, although spiders never develop wings.
Spiders grow by molting, or ecdysis. In this process, the spider casts off its tight outer body cover-its exoskeleton-after secreting a new, larger one underneath. Spiderlings gradually develop into adults in this way. Some color patterns are peculiar to certain species when they are spiderlings and change as they approach adulthood. Few spiders molt after sexual maturity, but some as female tarantulas, do.
All spiders exhibit similar premolting behavior. They do not eat, become lethargic and retreat into silken molting quarters in a burrow, under a leaf or in a corner. The outer skeleton splits along the upper body portions and the spider gradually slips its body and legs from the old casing, much like taking off a skin-tight glove. The actual molting process varies among species and can take from less than 15 minutes to a full day. Molting spiders are particularly vulnerable; they are unable to move away or fight back because they must rest until their new exoskeleton hardens.
Identification of spider species is generally difficult for the novice and expert alike. Spider classification is based on external structures that include eye arrangement, number of hairs and claws on the legs and the complicated structure of reproductive organs. Understanding the specialized technical vocabulary in many spider keys often requires the assistance of a biologist. Luckily, many Missouri arachnids are distinctive in color, shape, size and habitat. The photographs and descriptions here should help you identify some of Missouri's more common spiders.
Your next woodland walk offers the opportunity to make peace with these interesting creatures so undeserving of their fearful reputations. After all, a spider acts as a spider would.
