Spiders belong to the class Arachnida, encompassing over 48,000 known species globally. These eight-legged invertebrates are classified as generalist predators, consuming a wide variety of available prey. Their unique biological structure, particularly a narrow digestive tract, requires specialized methods for capturing and processing food. This anatomy necessitates liquefying their meals before ingestion. Spiders also rely on adaptations to acquire and conserve water, allowing them to thrive in diverse habitats.
The Predominantly Insectivorous Diet
The vast majority of spiders are carnivores, feeding primarily on insects and other small arthropods. Common prey items include flies, mosquitoes, moths, beetles, and sometimes other spiders. The size of the spider often determines the scale of its potential meal. While small species focus on tiny insects, larger spiders, such as tarantulas, prey on small vertebrates. These larger captures can include frogs, lizards, small fish, and occasionally bats or rodents.
Though almost all spiders are predators, the jumping spider Bagheera kiplingi, found in Central America, is a notable exception. It is considered the only species with a predominantly herbivorous diet, feeding mainly on Beltian bodies—protein- and sugar-rich nubs that grow on acacia plants. Even this botanical feeder occasionally supplements its diet by consuming nectar or ant larvae.
Diverse Hunting Strategies and External Digestion
Spiders utilize two main strategies to secure their meals, reflecting passive and active hunting styles. Passive hunters, such as orb-weaving spiders, construct intricate silk webs designed to intercept prey. Active hunters, like wolf spiders and jumping spiders, use speed, camouflage, and keen eyesight to stalk their food instead of relying on a snare. Once prey is secured, the spider uses its chelicerae, or fangs, to inject venom, which quickly immobilizes the prey.
The method of consumption is called external digestion, necessary because the spider’s narrow gut cannot process solid material. The spider expels a cocktail of digestive enzymes from its gut directly into the prey’s body. These chemicals quickly break down the internal tissues into a nutrient-rich liquid. The spider then uses a specialized sucking stomach to draw the liquefied tissues into its body. Many species repeatedly pump the digestive fluid back and forth to ensure maximum nutrient absorption before discarding the empty husk.
Sources of Hydration
All spiders require water, employing specialized methods to acquire and conserve this resource. A significant amount of moisture is obtained directly from the body fluids of their prey during external digestion. This fluid extraction provides both hydration and nourishment simultaneously. Spiders also seek out dedicated sources of free-standing water, drinking dew drops, raindrops, or condensation that collects on surfaces or their own webs. When drinking, they use their chelicerae to draw up the small water droplets.
Spiders possess physiological adaptations to minimize water loss. Their waxy exoskeleton acts as a protective barrier to prevent excessive evaporation. Furthermore, they excrete nitrogenous waste as uric acid, a nearly dry compound, which aids in water conservation.