Spiders are generalist predators, consuming a wide array of prey rather than specializing in one type of food. Their diet primarily consists of insects and other arachnids, but they are highly opportunistic, readily attacking any suitable prey they encounter. When people ask if spiders eat “worms,” they are usually referring to two distinct groups: true worms (segmented annelids like earthworms) and insect larvae (such as caterpillars or grubs). The answer depends entirely on which group is being discussed, as consumption patterns differ significantly across spider species.
The Direct Answer: Consumption of Earthworms and Annelids
True worms (phylum Annelida) are not a common staple in the diet of most spider species. The vast majority of spiders, particularly those relying on web-based traps, rarely encounter earthworms, which spend most of their lives burrowing underground. Earthworms also lack the hard exoskeleton many spiders prefer and are often too large for smaller spiders to subdue effectively.
Predation on earthworms is almost exclusively limited to larger, ground-dwelling spiders that actively hunt near the soil surface. This includes species such as large wolf spiders, trapdoor spiders, and mygalomorphs like tarantulas, especially those residing in humid tropical rainforests. Tropical species from the Theraphosidae (tarantulas) and Ctenidae (wandering spiders) families account for a significant percentage of recorded earthworm predation events. The giant tarantula, Theraphosa blondi, has even been documented consuming giant earthworms that can reach up to a meter in length in French Guiana.
For these larger, cursorial spiders, earthworms represent a high-protein, energy-rich meal, making them a profitable catch when encountered. While observed in both temperate and tropical regions, the consumption of earthworms remains an opportunistic behavior rather than a primary food source. Smaller spiders, like some crab spiders (Xysticus species), have occasionally been observed preying on much smaller earthworms, demonstrating that size and venom potency can sometimes overcome the challenge of a soft-bodied meal.
The Crucial Distinction: Spiders and Insect Larvae
The creatures most commonly eaten by spiders that are mistakenly called “worms” are insect larvae. These include caterpillars, grubs, waxworms, and mealworms, which are a common and important part of the diet for a wide range of spiders. Unlike earthworms, these larvae are often found above ground, feeding on foliage or in decaying matter, making them easily accessible to both web-building and hunting spiders.
Insect larvae are soft-bodied and lack the defensive speed and hard armor of adult insects, making them easier for a spider to immobilize and digest. A caterpillar caught in a sticky web, for example, is quickly wrapped in silk and dispatched, providing a substantial meal for a web-builder like an orb-weaver or a cobweb spider. The high nutritional content and ease of capture make these larval forms a favored prey item.
In laboratory settings and the pet trade, insect larvae like mealworms are commonly used to feed captive spiders, demonstrating their suitability across many spider families. The distinction is significant: while earthworms are an occasional, opportunistic meal, insect larvae are a regular and predictable component of many spiders’ natural diets.
Subduing and Digesting Large, Soft-Bodied Prey
Spiders have a unique method for processing large, soft-bodied prey that lacks a hard exoskeleton, such as earthworms and insect larvae. The first step in subduing such a meal is the injection of venom through their chelicerae (fangs). This venom quickly paralyzes the struggling prey and begins the process of external digestion.
Since spiders cannot chew solid food, they rely on extra-oral digestion. Digestive enzymes are either injected directly into the prey’s body or regurgitated onto its surface. These potent enzymes break down the internal tissues and organs, liquefying the contents into a nutrient-rich fluid.
The spider then uses a specialized sucking stomach to pump the liquefied meal into its digestive tract. For soft-bodied prey, this process results in the entire body cavity being emptied, leaving behind only the outer skin or cuticle. Tarantulas, which have larger chelicerae, often crush and manipulate the prey while digestion occurs, resulting in a small, dry ball of indigestible material left behind.