Spiders are obligate predators, meaning they must consume other organisms to survive. Their diet is governed by opportunistic hunting and size constraints. The collective impact of this predatory lifestyle influences terrestrial ecosystems across the globe. Nearly all of the over 50,000 known spider species rely on capturing live prey, utilizing specialized methods like venom and external digestion.
The Primary Diet of Spiders
The majority of a spider’s diet consists of other arthropods, primarily insects and smaller arachnids. Spiders are generalist predators, consuming almost any small organism they can subdue. Common prey items include flying insects like mosquitoes, flies, and moths, as well as crawling types such as beetles, ants, and grasshoppers. Many species also engage in arachnophagy, preying on other spiders, which regulates local populations. Spiders are effective controllers of pest populations, often targeting insects that feed on plants or carry diseases.
Hunting Strategies and Killing Mechanisms
Spiders employ two broad strategies: passive trapping and active hunting. Passive hunters, such as orb-weavers, construct intricate silk structures to intercept and entangle organisms. Active hunters, like wolf spiders and jumping spiders, rely on keen senses and speed to pursue, ambush, or leap onto their prey.
Once captured, the spider delivers a bite using its chelicerae (fangs) to inject venom that quickly immobilizes or kills the victim. This venom contains neurotoxins that disrupt the prey’s nervous system, preventing a struggle. Some venoms also contain enzymes that initiate tissue breakdown before the spider begins to feed.
The killing process concludes with extra-oral digestion. The spider pumps digestive fluids, rich in enzymes like proteases and lipases, into the immobilized prey’s body. These powerful enzymes liquefy the internal tissues, transforming the meal into a nutrient-rich liquid. The spider then sucks up this fluid, leaving behind only the empty exoskeleton or husk.
Killing Beyond Insects: Vertebrate Prey
While the primary diet is arthropods, a small number of large spider species occasionally kill and consume small vertebrates. This behavior is observed mostly in tropical or subtropical regions, involving large-bodied spiders, particularly tarantulas and wandering spiders. Prey items can include small frogs, lizards, snakes, fish, mammals, or birds.
The Goliath Birdeater tarantula, for example, has been documented preying on rodents and small snakes. These occurrences are rare, opportunistic events rather than regular dietary habits, often involving juvenile or injured vertebrates. The mechanism remains the same—venom injection followed by extra-oral digestion—but the spiders’ physical size and strength allow them to subdue much larger animals.
The Ecological Impact of Spider Predation
The collective predatory action of the global spider population represents a significant ecological force. Scientific estimates suggest that the world’s spiders kill a biomass of prey ranging from 400 to 800 million metric tons annually. This figure highlights their significance in maintaining ecological balance, especially concerning insect populations.
Over 90% of this volume of prey consists of insects and springtails, underscoring the role of spiders as the dominant terrestrial invertebrate predators. Spiders play an important part in forest and grassland biomes, where they account for the vast majority of the annual prey killed. Their widespread and constant predation serves as a natural form of pest control that benefits global ecosystems and agriculture.