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Garden spiders help control Missouri’s insect population

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Argiope

The argiope, or garden spider, is a major benefit to society by eating many insects.

Perhaps no arachnid symbolizes what’s wrong with many humans’ perception of spiders better than the garden spider.

This is the time of year when yellow garden spiders are frequently seen in this region. For many they’re a frightful sight. Walking up unexpectedly on this large yellow-and-black creature clutching firmly to its web with its thick, dark legs can put a quick step backwards into the stride of the most ardent nature lover. 

Watch what this spider eats over the course of a few days, though, and your fear will likely be replaced by appreciation. Unless, that is, you enjoy the flies, mosquitoes and other flying insects that buzz around your face and the grasshoppers that can harm gardens and crops.

Garden spiders are one of the approximately 480 species of spiders that reside in Missouri. They’re one of the better-known arachnids found in the state’s grasslands, but they are not the only spider commonly seen on a prairie. Far from it. Entomologists estimate that more than two million spiders may be found in a typical square acre of grassland. 

That kind of abundance may cause spider haters to shudder, but before you reach for the insecticide, consider this: Since each spider may consume one insect per day (and some eat more), think about the benefit the spiders living in that one acre of prairie can provide to humans in the form of controlling insect populations. Multiply that one acre by several or several hundred, and a good thing becomes a really good thing.

Moving back to garden spiders, as their name indicates, garden spiders aren’t limited to prairies. They also are familiar sights in gardens and flower beds, particularly at this time of year. The true name of the garden spider is argiope; “garden spider” is a collective term for spiders in the genus Argiope. Several species of argiopes live in North America.

Garden spiders, and all other types of spiders, are not insects. They are arachnids. They are classified in different biological groups. Spiders are in the Arachnida class and insects are in the Insecta class. Some of the most noticeable differences between these two classes are in physical appearance: Spiders have two main body parts, eight legs and no antennae; insects have three main body parts, six legs and antennae.

Garden spiders, as is the case with most spiders, do not live more than a year. After mating, the female spider lays eggs on one side of its web, then covers them with a papery sac. The egg sac, which can be up to one inch wide, may hold more than 1,000 eggs. The eggs hatch in the fall, but the young spiders stay inside the sac throughout the winter. In spring, the young spiders leave the sac in search of females and food.

Garden spiders,  like other spiders,  don’t eat their food in the same way you and I do. When an insect gets trapped in a web, it struggles to get free, creating vibrations that tell the spider something is caught. The spider quickly crawls to its prey and injects venom that paralyzes the insect and, at the same time, turns the insect’s insides into liquid. 

The spider wraps its prey in silk strands and proceeds to suck out the liquefied parts of the insect on the spot or carries it off to be enjoyed later. Though this manner of eating may sound disgusting to us, it helps control insect pests. Studies have shown, over the course of a summer, one spider will consume more insects than an insect-eating bird will.

There’s no unequivocal answer why grasslands — particularly prairies — attract large numbers of spiders, but it probably has to do with plant diversity. A native prairie contains a vast array of plants of varying sizes that have different types of blooms. This variety attracts a multitude of insect species, which makes it an ideal place for creatures that prey on insects.

More information on area spiders can be found at missouriconservation.org.

Francis Skalicky is the media specialist for the Missouri Department of Conservation's Southwest Region. For more information about conservation issues, call (417) 895-6880.

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