Wait, Don’t Kill It! Spiders Protect Us from Disease

Wait, Don’t Kill It! Spiders Protect Us from Disease

Frances Figart

By Frances Figart, Creative Services Director 

This time of year, some varieties of spiders may seek shelter from the cooler temperatures by coming into your house. If you find one, consider this before you take action: Most spiders are harmless, they provide essential services for humans, and they are actually critical for the balance of our ecosystems.

“Without spiders we would probably succumb to some nasty insect-borne disease while waiting to starve to death,” said Kefyn Catley, who has studied the evolutionary biology of spiders on four continents. Some of his work has been done in Great Smoky Mountains National Park, where a number of researchers have recorded 531 species of spiders, 41 of them new to science.

Kefyn Catley

For years Catley taught and conducted research as a professor of biology at Western Carolina University in Cullowhee, North Carolina. He was a research scientist at the American Museum of Natural History and has taught the “Spiders of the Southern Appalachians” course at Highlands Biological Station for the past 15 years.    

Spiders are part of a larger group of species called arthropods, which Catley—who holds a Ph.D. in arthropod systematics from Cornell—describes as the little and largely unseen creatures that run the world.

“Arthropods provide the life support systems that humans and the whole terrestrial biosphere rely on for their continued existence,” he said. “Without them it has been estimated that all almost all life on land—including humans—would go extinct in nine months.”

Spiders have two main body parts and two unique characteristics: silk produced through “spinnerets” located at the tip of the abdomen, and the male “pedipalp” as an organ for transferring sperm to the female.

“Spiders have an ancient lineage originating some 400 million years ago,” Catley said. “They are the largest and most important group of predators on the planet.”

These tiny creatures regulate all our land-based ecological systems by controlling herbivorous insect populations. It is estimated that the spiders on about two acres of forest in Western North Carolina can consume 48 metric tons (105,840 pounds) of insects in a year.

“Spiders also provide us with excellent models for studying ecology, biochemistry, competition, and sexual selection, among other fields,” said Catley who is retired but still teaches courses on spider biology and insect photography. “They contribute to research in pest control, venom chemistry, and the cloning of silk.”

Even with all of these benefits, many people are afraid of all spiders because a few have harmful bites. Catley points out that less than one percent of spider species are toxic to humans. Between 1979 and 1991, the United States saw 1,135 deaths attributed to lightning strikes, 591 attributed to bee stings, 72 to snake bites, and 57 to alleged spider bites—but as many as 80 percent of spider bites are wrongly diagnosed. This translates to a 20 times greater chance of being struck and killed by lightening than being killed by a spider!

Some spiders, like the cellar and parson varieties, live with us indoors all year round. If you protect your living space from pesticides, these constant companions will be at your service, significantly reducing your undesirable insect populations.

So, what should you do if you see a spider in your home? Catch it with a cup and postcard and put it out—or simply let it be.

Garden Spider Striped Jumping Spider Tan Jumping Spider
Garden Spider Argiope Aurantia Striped Jumping Spider Colonus Sylvania Tan Jumping Spider Platycryptus Undatus
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