Spiders are widely perceived as strict carnivores, predators that exclusively hunt and consume other living organisms. This common understanding largely holds true across the vast diversity of spider species. However, a closer look at their dietary habits reveals a more intricate picture, hinting at nuances beyond simple predatory behavior.
The Predatory Nature of Spiders
Most spider species are carnivores, feeding primarily on insects and other small arthropods. They acquire food through diverse methods, including web-building, active hunting, and ambush tactics.
Many spiders construct silk webs to ensnare prey like flies, mosquitoes, and moths. Once caught, the spider detects struggles through web vibrations and quickly immobilizes it.
Other spiders are active hunters, not relying on webs. Wolf spiders and huntsman spiders pursue prey using speed and agility. Ambush predators, like crab spiders, lie camouflaged on flowers or bark, striking precisely when an insect comes within reach.
Some spiders employ unique strategies, such as bolas spiders swinging a sticky silk ball to catch moths, or trapdoor spiders lurking in silk-lined burrows to pounce on passing prey.
How Spiders Feed
Spiders feed through external digestion, breaking down food outside their bodies. After capturing prey, spiders use their chelicerae, mouthparts tipped with fangs, to inject venom. This venom paralyzes or kills the prey.
Following venom injection, spiders release digestive enzymes into the prey’s body. These enzymes liquefy the prey’s tissues, turning them into a digestible “soup.” The spider then sucks up this liquid using a muscular sucking stomach.
This process allows spiders to consume prey larger than themselves, leaving behind only the exoskeleton. Some spiders, particularly mygalomorphs, may also use their chelicerae to mash and shred prey into a pulpy mass before ingesting the liquid.
The Rare Exception to the Rule
An exception to the predominantly carnivorous spider diet exists: Bagheera kiplingi. This jumping spider, found in Central America, has a largely plant-based diet. Its primary food source is Beltian bodies, specialized, protein- and sugar-rich nubs on acacia plant leaflets and leaf stalks.
Beltian bodies are part of a mutualistic relationship between acacia plants and ants, where ants protect the plant in exchange for these offerings. Bagheera kiplingi exploits this, skillfully avoiding guarding ants to access Beltian bodies.
While predominantly herbivorous, Bagheera kiplingi may occasionally supplement its diet with acacia nectar, small insects, or ant larvae. This challenges the understanding that all spiders are strict predators.
Other Dietary Components
Beyond their primary prey or specialized plant matter, spiders may consume other substances. Water is important for their survival; much hydration comes from prey, but spiders also drink freestanding water, dew, or condensation. They can also sip water using their mouthparts.
Some spider species, even carnivorous ones, have been observed to incidentally consume plant-based materials like nectar or pollen. Nectar provides sugar, and pollen caught in webs may be ingested when spiders recycle silk. These plant materials are supplementary to their main diet and not a primary food source for most species.