What Do Spiders Eat? Insects, Other Spiders and Even Plants

Insects: the main course

Almost all of the world’s roughly 50,000 known spider species are carnivores, and insects are by far their most important food. Web builders catch flying insects such as flies, mosquitoes, moths, bees and wasps, while ground hunters take crickets, beetles, cockroaches and ants. Springtails and mites, tiny soil animals, are also eaten in huge numbers.

The scale is remarkable. A 2017 study estimated that the world’s spiders kill between 400 and 800 million tonnes (440–880 million US tons) of prey every year. That is comparable to, or more than, the total weight of meat and fish eaten by all people each year. Most of this prey was estimated to be caught in forests and grasslands, and the study noted that spiders are among the most important insect predators on land.

What different spiders eat

What a spider eats depends on how it hunts and how big it is.

The European garden spider waits in its web for flying insects to blunder in, wraps them in silk and bites them. The Carolina wolf spider, by contrast, builds no capture web and runs down or ambushes prey on the ground at night. Web builders take what the web catches, while hunting spiders can be more selective.

Spiders that eat other spiders

Spiders are a regular part of many spiders’ diets. Small spiders are caught in the webs of larger ones, and hunting spiders readily attack other spiders. Some groups specialize in this. Pirate spiders creep into other spiders’ webs and pluck the threads to lure out the owner, and some tropical jumping spiders hunt web-building spiders with remarkable cunning.

Cannibalism within a species also happens, most famously when females eat males during or after mating. It is common in some species and rare in others.

Frogs, fish, bats and birds

Large spiders can overpower vertebrates. Researchers who reviewed reports worldwide found that spiders catching small fish have been recorded on every continent except Antarctica, mostly by fishing spiders that hunt at the water’s edge. Spiders catching bats, usually small bats tangled in large orb webs or seized by big hunting spiders, have also been documented on several continents.

Tarantulas and other big spiders eat frogs, lizards and small snakes now and then. The goliath birdeater of South America got its name from an old illustration of a spider eating a bird, but in reality birds are an unusual meal. Even for the biggest spiders, insects and other invertebrates make up almost all the food.

A spider that eats plants

The great exception is Bagheera kiplingi, a small jumping spider from Mexico and Central America. It lives on acacia trees that are guarded by ants. The trees produce tiny, protein-rich leaf tips called Beltian bodies to feed the ants, and the spider sneaks past the guards to eat them. In one Mexican population, plant food made up about 90 percent of its diet.

Other spiders take plant food only occasionally. Some jumping spiders sip nectar, and young orb weavers that eat their old webs swallow pollen grains stuck to the silk, gaining a small extra source of protein.

How do spiders eat?

Spiders cannot chew and swallow solid food. They bite prey with their fangs, which inject venom to paralyze or kill it. Then they bring digestive juices into contact with the prey. These juices dissolve the soft tissues, and the spider sucks up the liquid through a narrow mouth and a pumping stomach, leaving a dry husk behind. Some spiders mash the prey with their jaws while digesting it.

Web builders often wrap prey in silk first, which keeps a struggling insect safe to bite and lets the spider store it for later. This is one reason webs are so effective, explained in how spiders spin webs.

Spiders are good at surviving between meals. Their slow metabolism lets many species go for weeks without food, and big spiders can last for months. When food is plentiful, a spider can eat a meal that is large compared with its own body.