Spiders are a diverse order of arthropods found on every continent except Antarctica. They are defined by eight legs, two main body segments, and a universally predatory lifestyle. With over 40,000 described species, spiders are among the most abundant terrestrial predators globally. Their complex diet and specialized hunting methods reveal a highly specialized group of animals.
The Primary Spider Diet
The vast majority of a spider’s diet consists of insects and other small arthropods. This food source includes common prey like flies, moths, beetles, and mosquitoes, which are intercepted in webs or actively pursued. Spiders also prey upon other arachnids, such as mites, smaller spiders, and harvestmen, depending on their size and hunting style.
A spider’s diet is heavily influenced by its body size and the microhabitat it occupies. Smaller spiders tend to focus on tiny, soft-bodied insects like springtails and gnats, which are easier to subdue and digest. Conversely, larger spiders are capable of consuming bigger, harder-shelled prey like large beetles, crickets, and cockroaches.
The prey spectrum of web-building species is largely determined by the availability of prey in the immediate vicinity of their silk traps. An orb-weaver spider, for instance, primarily catches flying insects that happen to collide with its web. Spiders living in forest litter or under stones consume ground-dwelling arthropods that pass by their burrows or sheet webs.
Hunting Strategies and Prey Capture
Spiders utilize two broad but distinct strategies for prey capture: passive web entrapment or active hunting. Web-building spiders create elaborate silk structures that function as non-selective air filters to intercept flying or walking prey. Orb-weaver spiders construct the familiar circular nets, which are effective at capturing insects with their sticky threads.
Other web architects employ different designs, such as the sheet web spiders that spin flat, horizontal silk mats over vegetation. These spiders wait beneath the sheet, sensing vibrations from insects that fall onto the mat. Funnel-web spiders construct a tube-shaped retreat with a sheet of silk extending outward, using the silk as a tripwire to signal the presence of prey.
Active hunters forego silk traps entirely, relying instead on stealth, speed, and acute sensory perception. Wolf spiders are swift, ground-dwelling hunters that chase down their prey over short distances. Jumping spiders, known for their excellent vision, stalk their victims before pouncing on them with impressive accuracy.
Ambush predators, such as crab spiders, wait patiently on flowers or foliage that match their own coloration. They use their strong front legs to quickly grasp an unsuspecting insect visitor, such as a bee or butterfly. Once the prey is secured, nearly all spiders use venom, which is injected through their fangs, to quickly paralyze or kill the captured meal.
The venom is a complex cocktail of neurotoxins and other compounds designed to rapidly incapacitate the prey’s nervous system. This swift immobilization prevents the prey from damaging the spider or escaping. In some species, the venom also contains digestive enzymes that begin the liquefaction process before the spider starts feeding.
Unique Feeding Mechanics
Once the prey is subdued, the spider initiates external, or pre-oral, digestion. Spiders possess a very narrow gut, making the ingestion of solid food structurally impossible. They must first liquefy the internal tissues of their prey.
The spider accomplishes this by pumping a mixture of potent digestive enzymes from its midgut into the body of the captured animal. This enzymatic cocktail typically includes proteases, lipases, and nucleases, which work together to break down the prey’s proteins, fats, and nucleic acids. These enzymes dissolve the internal structures, effectively turning the prey into a nutrient-rich liquid “soup.”
The process often involves the spider regurgitating and re-sucking the digestive fluids, which helps to thoroughly mix the enzymes within the prey’s body cavity. After the internal tissues have been completely dissolved, the spider uses a muscular, pumping stomach to suck the liquefied meal back into its own digestive tract.
All that remains after feeding is a dry, empty husk of the prey’s exoskeleton. This consumption method is highly efficient, allowing spiders to extract maximum nutrients while avoiding indigestible solid matter.
Dietary Exceptions and Non-Arthropod Meals
While insects and other arthropods form the bulk of the spider diet, some larger species have been documented consuming small vertebrates. Large tarantulas and other sizable hunting spiders are known to prey on small lizards, frogs, mice, and even small birds, which they are able to overpower and inject with potent venom.
These instances of vertebrate predation are opportunistic, occurring when the spider encounters a suitable small animal near its lair or hunting ground. The ability to consume such diverse prey is a function of the spider’s size and the strength of its venom and chelicerae.
A remarkable exception to the general carnivorous rule is the Central American jumping spider Bagheera kiplingi, which is predominantly herbivorous. This tiny species derives over 90% of its diet from Beltian bodies, which are protein and lipid-rich plant structures found on acacia trees.
The spider must skillfully avoid the aggressive ants that typically guard these plant structures. While B. kiplingi occasionally supplements its diet with nectar or ant larvae, its primary consumption of plant material makes it a unique dietary outlier.