These two numbers prove how much we depend on wild animals

Jumping spiders in the family Salticidae, like this one, are known to prey on crop pests. | Jan Rozehnal/Getty Images/iStockphoto

A new study shows how wild predators like spiders support human food systems.

For those of us who live in a city or suburb and don’t farm our own food, it can be hard to understand how wild animals affect our lives. Natural resources like fresh drinking water and vegetables are just sort of ... there. Water comes out when you turn on the tap. Grocery store shelves are stocked with produce.

But without ecosystems and the animals that occupy them, many of these resources would be far less accessible — and some, like chocolate, might not even exist at all. Spiders that we may find icky eat pests that would otherwise damage the foods we buy at the store, as do adorable owls. American kestrels, meanwhile, are known to eat or scare away birds and other pests that consume fruit on orchards.

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A female American kestrel.

Just how useful wild animals are to us — from a purely selfish perspective — can be hard to quantify. But a new study, published today in the Proceedings of the Royal Society B, offers some clarity into the role native species play in safeguarding our food system.

The study, a meta-analysis that reviewed dozens of past experiments worldwide, explores how native predators, including birds and various insects, help limit pests such as aphids and moths that damage crops. The results are pretty remarkable, as revealed by two key numbers:

73 percent

Wild predators, including birds and insects, reduced pest populations on farms by almost three-quarters on average, according to the study.

Farms with wild predators, often found naturally in and around a farm, have around 73 percent fewer pests. Birds, beetles, spiders, and other predatory insects drive down the number of harmful pests, the study found.

The study did not find evidence that bats control pests, perhaps due to limited data, though these flying mammals do consume large quantities of insects at night. (It’s also worth noting that meta-analyses, in general, sometimes produce exaggerated results due to “publication bias” — basically, researchers are more likely to publish their work if it shows a significant result in one direction or another. Experiments that don’t yield compelling results often get left out of these sorts of analyses.)

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A running crab spider of the Philodromidae family preying on a carpenter ant of the genus Camponotus.

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A female Carolina mantis. Praying mantises are among the many beneficial insects that help control pests.

25 percent

The amount by which wild predators increased crop yield, or a farm’s production, on average.

Predators are consuming pests that would otherwise eat away at the farm’s production. Basically, all the animals that are flying, buzzing, and crawling around farms end up making those farms more productive.

“Natural predators are another tool in the toolkit of farmers who try to reduce crop losses to pests,” Catherine Lindell, an associate professor of biology at Michigan State University, said by email. (Lindell was not affiliated with the study.) “Enhancing landscapes and habitats for natural predators may improve their likelihood of reducing pests to an even greater degree.”

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Ladybug larva eating an aphid, a common crop pest.

Relying on native predators to eat pests comes with a number of other benefits. Unlike many chemical pesticides commonly sprayed on farms, wild animals typically don’t pose a risk to human health or the environment. Plus, wild predators control pests for free (although sometimes farmers will boost their pest-control services by introducing more of a certain predator to a farm — and that, of course, does cost money and time).

The bottom line is that by keeping native ecosystems intact — such as by reducing pesticide use and leaving some native vegetation in place — these predators can do their job, and that job benefits us all.