Spiders, belonging to the class Arachnida, are one of the most successful and widespread groups of predators on Earth, having adapted to nearly every terrestrial habitat globally. As the largest order of arachnids, with over 50,000 recorded species, their existence is primarily defined by their hunting success. This population of eight-legged carnivores plays a fundamental role in maintaining the balance of ecosystems through their diverse and specialized diets. Their survival strategies, which range from passive web-building to active pursuit, all revolve around securing a steady supply of animal protein.
The Primary Diet Arthropods and Invertebrates
The majority of spider species rely on a diet consisting of arthropods and invertebrates. Insects, such as flies, moths, beetles, and crickets, form the bulk of the global spider diet. The menu extends to other arachnids, including mites, scorpions, and even other spiders through cannibalism, depending on the species and environment. The prey captured is typically determined by what the spider can physically subdue, meaning size is the primary constraint.
The ecological impact of this focused predation is immense, as spiders collectively consume an astonishing amount of prey each year. Researchers estimate that the world’s spider community devours between 400 and 800 million metric tons of insects and other invertebrates annually. This massive consumption rate demonstrates the spiders’ disproportionate role in pest control, managing insect populations worldwide. Their diet is opportunistic, capturing whatever small creature they encounter.
How Spiders Consume Their Prey
Unlike mammals, spiders cannot chew or swallow solid food, necessitating a unique physiological process known as external digestion. Upon capturing prey, most spiders first inject venom through their fangs, which quickly paralyzes or kills the victim. The hollow fangs act like hypodermic needles to deliver this immobilizing cocktail.
Following the initial attack, the spider introduces potent digestive enzymes directly into the prey’s body. These enzymes work to break down the captured animal, liquefying the contents from the inside out. The spider then uses a strong sucking stomach to pump the resulting liquid into its digestive tract. This leaves behind only the empty exoskeleton of the prey, which is discarded.
Some species may also use their chelicerae to grind the prey into a pulp while simultaneously flooding it with enzymes before ingestion. The narrow gut of the spider is adapted to handle only this pre-processed liquid food, preventing any solids from entering the digestive system. This specialized method of fluid intake is a defining characteristic of nearly all spiders.
Hunting Larger Vertebrate Animals
Although the staple diet consists of invertebrates, some of the larger spider species are capable of preying on small vertebrate animals. This occurs primarily in large mygalomorphs, such as various tarantula species, and specialized hunters like fishing spiders. These opportunistic kills typically occur when a small animal wanders too close to the spider’s burrow or hunting ground.
The Goliath birdeater, despite its name, rarely consumes birds but is known to take small lizards, mice, frogs, and even small snakes. Fishing spiders, belonging to the Dolomedes genus, are semi-aquatic hunters that position themselves near water to detect vibrations caused by aquatic prey. These spiders have been documented successfully capturing small fish and tadpoles using specialized venom potent against aquatic organisms. Such predation events are less frequent than insect consumption but highlight the impressive predatory capabilities of the largest arachnids.
Unexpected Dietary Exceptions
While nearly all spiders are obligate carnivores, a few species have evolved to include non-animal matter. The most striking example is the Central American jumping spider, Bagheera kiplingi, which is the only known spider with a predominantly herbivorous diet. This species feeds primarily on Beltian bodies, which are protein and fat-rich nodules found on the leaves of acacia plants.
In some regions, these plant-based Beltian bodies can make up over 90% of the Bagheera kiplingi diet. Beyond this unique example, many spider species are known to occasionally supplement their diet with plant fluids. They may sip on flower nectar, plant sap, or even ingest pollen that becomes trapped in their webs. These plant supplements provide sugars and other micronutrients, but they remain secondary to animal protein.