Spiders have the most unfair rep of all, at least according to Norman Platnick, curator emeritus of spiders at the American Museum of Natural History in New York City. "If there were no spiders, it's not certain there would be any of us," Platnick says. That's because of their incredible appetites. Dozens of spider species devour insects that would otherwise wreak havoc on our food supply.
Just how much they eat has been hotly debated. In the 1940s, British arachnologist W. S. Bristowe famously estimated 2.2 billion spiders in the United Kingdom, eating at minimum 100 insects per year, for an annual consumption of at least 220 billion insects. He later wrote the oft-quoted line that the weight of insects eaten by British spiders exceeds the combined weight of all British people. Thirty years later, another researcher made a similarly grand estimate, calculating that every year, spiders eat an average of 93,500 pounds of insects for every hectare of agricultural land. More recent studies suggest that it's more like 80 pounds per hectare per year, but that's still quite impressive.
Platnick, who has tracked down spiders in Chile, New Zealand, and Equador, among other places, proudly rattles off some of the creatures’ other benefits. Most spiders use venom, of all different types, to paralyze their prey. Some researchers are considering these compounds for medical use, such as anti-seizure drugs. And all species make silk that's both strong (with tensile strength greater than steel) and lightweight, providing a natural library of potentially useful materials. "If you could develop an equivalent manmade fabric, the uses are immense," Platnik says, "from parachutes from bulletproof vests." Something to think about, perhaps, the next time you're thinking of squashing one.