Spiders are major predators, but they are also a significant food source within the ecosystem. The life of an arachnid is constantly threatened by diverse insects that have evolved to hunt, parasitize, or opportunistically consume them. These insect antagonists employ methods ranging from immediate, paralyzing strikes to slow, methodical consumption, demonstrating specialized insect-spider relationships.
Highly Specialized Wasp Hunters
The most dramatic examples of insects that kill spiders belong to the family Pompilidae, commonly known as Spider Wasps. These highly specialized hunters dedicate their entire reproductive cycle to securing spider prey, such as wolf spiders, huntsman spiders, or tarantulas.
Once the spider is located, the wasp delivers a precise, paralyzing sting. The venom immobilizes the arachnid but keeps it alive and fresh for the wasp’s future offspring. The female wasp then drags the incapacitated spider to a prepared burrow or nest site.
Inside the chamber, the wasp lays a single egg onto the spider’s abdomen. When the larva hatches, it consumes the still-living, paralyzed host. The larva feeds on non-essential tissues first, avoiding vital organs until the last moment. This methodical consumption provides a sustained source of fresh nutrients until the larva is ready to pupate.
Insects That Use Spiders as Hosts
Parasitoids are a distinct group of insects that use spiders as hosts for their developing young without immediate paralysis. Certain Ichneumonidae wasps, such as the Polysphincta group, are ectoparasitoids. The female wasp lays an egg on the spider’s exterior, and the hatched larva slowly feeds on the spider’s hemolymph while the host continues to live.
Small-headed flies in the family Acroceridae also parasitize spiders. Adult acrocerids lay numerous eggs, and the tiny, mobile first-instar larvae (planidia) actively search for a host. Once a planidium finds a spider, it burrows inside, often lodging near the book lungs, sometimes remaining for years before completing development.
Some ichneumonid parasitoid larvae can chemically influence the spider’s behavior before consumption. The spider is induced to weave a final, unique web designed to protect the wasp’s pupa after the larva consumes the host. Both ichneumonid wasps and acrocerid flies cause a slow death, consuming the spider entirely just before pupation.
Opportunistic Insect Predators
Many generalist insect predators kill and consume spiders opportunistically. These insects do not rely on spiders as their sole food source but readily take them as prey.
The Praying Mantis is a well-known example, using its powerful, spiked forelegs to ambush and grasp various spider species. Large ground beetles (Carabidae) are effective, nocturnal predators that include smaller, vulnerable spiders in their varied diet. Aggressive ant species, such as army ants or fire ants, may overwhelm and kill spiders through sheer numbers, especially if the spider is defenseless or molting.
The Role of These Insects in Ecosystems
Insects that prey on spiders play a significant part in maintaining the balance of terrestrial ecosystems. Spiders are major predators, consuming thousands of insects annually, which helps regulate populations of herbivorous and pest species.
In turn, specialized and generalist insect predators regulate spider populations. This multi-layered predation supports overall biodiversity by preventing any single group from dominating. For example, the regulating pressure of spider wasps prevents certain spider populations from exploding, which serves as a natural form of biological control.