Pests: What's Their Purpose, Anyway?

Pests do have a purpose, and it's not just to bother humans.

As spring approaches and gardeners prepare to cultivate -- and battle pests -- you may start to wonder why are these pests around anyway? What's their purpose? It turns out they have have their roles.

Cockroaches might seem invincible, but there's a reason why they are hiding out in homes -- they're good eats. Neurobiologist Friedrich Barth of the University of Vienna studies spiders and told Discovery News that many spiders eat cockroaches. Centipedes, ants, scorpions, frogs, lizards, birds, snakes and mice also eat them.

The earliest known bed bug fossils date to 1352 B.C. and were discovered at an Egyptian archeological site, according to the book "Bed Bug: The Return of the World's Most Reviled Household Pest." The parasitic insects likely existed before then, however, and opportunistically infested humans and bats in caves. Bed bugs have evolved to prey upon us, so they are here because we are here too. Like any species low on the food chain, bed bugs can nourish other organisms, such as centipedes. Animals like birds and toads, in turn, eat centipedes. Parasites can also get parasites, such as parasitic bacteria, which would bite the dust if their host went extinct.

Mosquitoes, both as adults and in their larval stage, are food for many species. For example, Steve Heydon, senior museum scientist at the Bohart Museum of Entomology, University of California at Davis, told Discovery News that wolf spiders love to eat mosquitos. "Wolf spiders are like mini tigers that run and pounce on prey at night," he said. Homeowners hoping to have fewer mosquitoes would do well not to spray for spiders, since spiders eat mosquitoes and other potentially disease-carrying insects.

Flies are among the most common insects that visit and pollinate flowers. Hearty flies are present at all times of year, so they become all the more important as pollinators for plants that flower during winter and fall. Some plants are even completely dependent upon flies for pollination.

Birds and bees -- along with bats, rodents and many others -- are important pollinators. Some beautiful flowering trees, such as those in the genus Butea, rely heavily on squirrels for pollination. Scientists are studying some Butea species for possible treatments for diabetes, liver disorders and other health problems.

Termites are nature's great recyclers. Outside of homes, they help to convert plant cellulose into compounds that can be recycled into the ecosystem to support new plant growth. In terms of what species eat termites, it is almost easier to ask what doesn't consume them, since termites are a common food source for numerous insects and animals. Primate culture and tool usage might have even evolved around termites. Chimpanzees, for example, feast on termites so much that they have devised brush-tipped fishing sticks to probe mounds for them.

Yellow jackets can become nuisances or even dangers near homes, particularly on warm days when they tend to come out of their nests. They serve as pollinators, though, and prey upon certain plant-eating bugs. A study led by Erin Wilson of UC San Diego and published in the journal Proceedings of the National Academy of Sciences also found that yellow jackets could indirectly benefit some native species by consuming non-native (i.e., invasive) predators of those species.

Swarming locusts have bothered humans for so long that these insects are even mentioned in the Bible. Exodus 10 refers to a "plague of locusts," for example. There is an effort now, however, to save the locust from pesticides and other threats. Studies have shown that locust grazing helps many plant species and can even lead to reduced fire risk on roadsides. Locusts provide food for wildlife, help to control weeds and benefit ecosystems in many other ways.

Humans are responsible for Africanized a.k.a. "killer" bees, due to interbreeding of honeybees from Europe and southern Africa. But Africanized bees have their good points, according to The New Agriculturalist, a publication funded by the UK Department for International Development. Killer bees "do better than European bees in tropical climates, they are less susceptible to some widely used insecticides and, most usefully, they are resistant to the varroa mite. Brazilian beekeepers have no need to spray against the mite and can sell their honey as pesticide-free."

Stinkbugs are agricultural pests and they do literally give off a strong odor when disturbed. The good news is that many stinkbug species prey on caterpillars, aphids and other soft-bodied, plant-eating insects. In Laos, some stinkbugs are edible (such as the species

Encosternum delegorguei

) and are regarded as culinary delicacies due to their pungent odor and taste, which has been likened to cilantro. Today's pest, in this case, might be tomorrow's food trend.