Spiders are predators within diverse ecosystems. These eight-legged arthropods consume vast amounts of prey annually, playing a significant role in ecological balance. Their diet varies by species, size, and habitat, but all use a unique method of consumption.
The Staple Diet: Insects and Other Arthropods
Most spiders prey on insects and other small arthropods. Common targets include mosquitoes, flies, beetles, crickets, and moths. Annually, spiders collectively consume an estimated 400 to 800 million metric tons of insects.
Spiders use diverse hunting strategies. Some build webs to ensnare flying insects in sticky silk. Others, like wolf and jumping spiders, are active hunters, relying on speed, agility, or eyesight to stalk and pounce. Spiders are beneficial as natural pest controllers in various environments, including agricultural settings and homes. Their diet helps regulate insect populations, including those that might otherwise damage crops or transmit diseases.
Beyond the Usual: Larger and More Diverse Prey
While insects are their main diet, some larger spiders prey on more substantial animals. Tarantulas, for example, consume small vertebrates like frogs, lizards, birds, rodents, and even small snakes. The Goliath birdeater, a large South American tarantula, is one such species whose diet can include small birds.
Fishing spiders, belonging to the genus Dolomedes, demonstrate another example of diversified diets. These semi-aquatic spiders hunt near water bodies, capturing not only aquatic insects but also small fish, tadpoles, and frogs. They often position themselves with their front legs resting on the water’s surface, detecting vibrations from passing prey before striking. Spiders also engage in cannibalism, with some species preying on other spiders, including those of their own kind.
The Rare Exception: Plant-Eating Spiders
Despite their predominantly carnivorous nature, the jumping spider Bagheera kiplingi is a notable exception. This Central American species is unique for its largely herbivorous diet, primarily feeding on specialized plant structures called Beltian bodies. These protein- and fat-rich nubs are produced by acacia plants as part of a mutualistic relationship with ants.
Bagheera kiplingi also consumes acacia nectar and occasionally supplements its diet with ant larvae. While other spider species might incidentally ingest pollen or fungal spores caught in their webs, or even nectar, Bagheera kiplingi is the only known spider to actively consume solid plant matter as its primary food source. This adaptation allows it to utilize a consistent food source, particularly in regions where insect prey might be scarce.
How Spiders Process Their Food
Spiders possess a distinctive method of consuming their prey, known as external digestion. After capturing prey, most spiders inject venom through their fangs. This venom immobilizes prey and begins liquefying internal tissues.
Once the prey is subdued, spiders regurgitate digestive enzymes from their midgut onto or into the prey’s body. These powerful enzymes break down the prey’s soft tissues into a liquid or semi-liquid form. Spiders then use a muscular “sucking stomach” to draw the liquefied contents into their narrow gut, leaving behind only the indigestible hard parts. This unique digestive process allows spiders to consume food that their narrow internal structures cannot otherwise accommodate.