Spiders are predatory creatures with diverse eating habits. Understanding their diet provides insight into their ecological importance and dispels common misconceptions.
The Primary Diet of Spiders
Most spiders are carnivores that primarily consume insects and other small arthropods. Their diet commonly includes flies, mosquitoes, moths, beetles, ants, and sometimes even other spiders. Spiders are abundant, with estimates suggesting there are an average of 131 spiders per square meter in some areas, increasing to 152 in grasslands.
Collectively, spiders consume an astonishing amount of prey, estimated to be between 400 and 800 million metric tons of insects annually. To put this into perspective, humans consume approximately 400 million tons of meat and fish each year. While many spiders are “sit-and-wait” predators, using intricate webs to ensnare their victims, others are active hunters, such as wolf spiders and jumping spiders, which pursue and pounce on their prey.
How Spiders Consume Their Prey
Spiders do not chew their food in the way many other animals do, as their guts are too narrow to process solids. Instead, they employ a process known as external digestion. After capturing prey, typically with silk or by direct attack, most spiders inject venom through their fangs, which are part of their chelicerae. This venom often paralyzes or kills the prey.
Following envenomation, spiders release digestive enzymes from their midgut onto or into the prey. These enzymes break down the internal tissues of the prey, liquefying them. The spider then sucks up this nutrient-rich liquid, leaving behind the indigestible exoskeleton. The pedipalps, a pair of appendages near the mouth, assist in manipulating the food during this process.
Beyond Insects and Common Misconceptions
While insects form the bulk of a spider’s diet, some larger species occasionally prey on small vertebrates. These rare instances can include frogs, lizards, small birds, fish, and even rodents. However, such occurrences are not common and are generally observed in larger spiders, particularly in tropical regions.
Some spider species also supplement their carnivorous diet with plant materials. This can include nectar, plant sap, pollen, and even specialized plant structures. For example, the jumping spider Bagheera kiplingi is notable for its largely herbivorous diet, primarily feeding on Beltian bodies from acacia plants.
A pervasive misconception is that spiders frequently crawl into human mouths during sleep. This is not supported by scientific evidence. Spiders are highly sensitive to vibrations and typically avoid large, noisy creatures like sleeping humans. They are not interested in consuming humans, and any bites are defensive reactions, not attempts at predation. Spiders play an important ecological role, primarily as predators of pest insects.