Caterpillars are one of the most heavily preyed-upon creatures in the natural world. Birds, insects, spiders, parasitic wasps, flies, reptiles, and small mammals all feed on them regularly. Their soft bodies and slow movement make them easy targets, and they’re packed with protein and fat, which is why so many animals depend on them as a food source.
Birds: The Biggest Caterpillar Predators
Songbirds are by far the most significant caterpillar predators on the planet. Ninety-six percent of terrestrial songbirds rely on caterpillars to feed their young. Nestlings need protein-dense, soft-bodied food to grow quickly, and caterpillars fit that requirement perfectly. Warblers, wrens, bluebirds, robins, sparrows, vireos, and tanagers all hunt caterpillars intensively during breeding season.
The numbers involved are staggering. A single pair of chickadees needs between 6,000 and 9,000 caterpillars in one season to raise a brood of five chicks. Multiply that across every nesting songbird in a forest or backyard, and caterpillars become the foundation of the food web during spring and summer. Most songbirds won’t even nest in habitats that lack caterpillars, because without them, there simply isn’t enough food to raise a family.
Cuckoos are notable for eating caterpillars that other birds avoid, including hairy and spiny species. Woodpeckers peel bark to find caterpillars hiding underneath. Even hummingbirds, known for nectar feeding, catch small caterpillars to supplement their diet and feed their young.
Predatory Insects and Spiders
A wide range of invertebrates eat caterpillars at every stage of growth. These predators often get overlooked because they’re small and work quietly, but collectively they kill enormous numbers of caterpillars in gardens, farms, and wild habitats.
- Assassin bugs are generalist predators that stab caterpillars with a sharp, needle-like mouthpart and drain their fluids. Some species can take down prey up to six times their own size.
- Predatory stink bugs (not the plant-feeding kind) use a stout piercing mouthpart to extract fluid from caterpillars and beetle grubs.
- Big-eyed bugs feed on moth eggs, small caterpillars, thrips, and mites using similar piercing-sucking mouthparts.
- Ground beetles are nocturnal hunters that patrol soil and leaf litter, catching caterpillars that feed at night or drop from plants.
- Ladybird beetles are best known for eating aphids, but many species also consume small caterpillars, insect eggs, and beetle grubs.
- Lacewings in their larval stage are voracious predators sometimes called “aphid lions,” and they readily eat small caterpillars too.
- Spiders catch caterpillars both in webs and through active hunting. Orb weavers trap them in silk, while jumping spiders and crab spiders ambush them on leaves and flowers.
Paper wasps are another important predator. They chew caterpillars into a pulp and carry the pieces back to their nests to feed developing larvae. A single paper wasp colony can remove hundreds of caterpillars from a garden over the course of a summer.
Parasitoid Wasps and Flies
Some of the most effective caterpillar killers don’t eat them outright. Instead, they develop inside the caterpillar’s body, consuming it from within. These are parasitoids, organisms that live as parasites during their larval stage but ultimately kill their host.
Parasitoid wasps, including the well-known braconid and ichneumonid families, lay their eggs on or inside caterpillars. The wasp larvae hatch and feed on the caterpillar’s internal tissues while it’s still alive. The caterpillar continues eating and moving for days or even weeks before the wasp larvae finish developing, kill the host, and emerge to pupate. If you’ve ever seen a caterpillar covered in tiny white cocoons, those are braconid wasp pupae.
Tachinid flies use a similar strategy with some fascinating variations. A female tachinid fly may insert eggs directly into the caterpillar’s body, glue eggs onto the caterpillar’s head or thorax, or even lay eggs on plant leaves so that a feeding caterpillar swallows them unknowingly. Once inside, the fly larva chews into the caterpillar’s tissues and breathes through small holes it opens in the host’s skin. If multiple eggs end up in a single caterpillar, only one fly larva survives to maturity. After the caterpillar pupates, the fly larva kills it, then either exits to pupate nearby or pupates inside the dead host.
Other Predators
Reptiles and amphibians eat caterpillars opportunistically. Lizards, particularly anoles, skinks, and geckos, snatch caterpillars from leaves and branches. Frogs and toads eat caterpillars they encounter on the ground or on low vegetation, especially at night. Small mammals like shrews, mice, and bats also consume caterpillars when available. Shrews in particular have extremely high metabolisms and eat nearly their body weight in insects daily.
How Caterpillars Defend Themselves
Given the sheer number of things trying to eat them, caterpillars have evolved an impressive range of defenses. The most sophisticated is chemical sequestration: absorbing toxic compounds from the plants they eat and storing those chemicals in their skin or blood to make themselves poisonous or foul-tasting to predators.
Monarch butterfly caterpillars are the classic example. They feed on milkweed and accumulate cardiac glycosides, compounds that cause nausea and heart problems in birds that eat them. After one bad experience, a bird learns to avoid the distinctive orange-and-black pattern. Cinnabar moth caterpillars store alkaloids from ragwort plants. Burnet moth caterpillars accumulate cyanide-releasing compounds from their host plants and maintain an extremely alkaline gut (pH 10.6) that prevents those compounds from activating prematurely and poisoning the caterpillar itself.
Beyond chemistry, caterpillars use camouflage, mimicry, and physical deterrents. Some resemble twigs, bird droppings, or leaf edges. Others have eyespots that make them look like snakes. Hairy and spiny caterpillars are difficult for many birds to swallow. Some species thrash violently, drop from their perch on a silk thread, or regurgitate foul-smelling fluid when disturbed. Swallowtail caterpillars have a forked, brightly colored organ behind their head that they inflate when threatened, releasing a strong odor.
Supporting Caterpillar Predators in Your Yard
If you’re dealing with caterpillar damage in a garden, working with natural predators is one of the most sustainable approaches. Planting native plants is the single most effective step, because native plants support native caterpillar species, which in turn attract nesting birds. Non-native ornamental plants support far fewer caterpillars, which means fewer birds stick around to provide pest control.
You can also attract and support beneficial insects by planting flowers that provide nectar and pollen for adult predators and parasitoids. Cilantro, fennel, buckwheat, sweet alyssum, and marigolds all help sustain populations of parasitoid wasps, tachinid flies, lacewings, and predatory beetles. Letting some areas of the garden stay a little wild gives ground beetles and spiders places to shelter.
For more targeted control, predatory insects like spined soldier bugs can be purchased from commercial insectaries. Buying directly from the producer rather than a distributor generally ensures better quality. Selective pest management tools that spare beneficial insects, such as products based on the naturally occurring bacterium Bt, kaolin clay barriers, and pheromone traps, help keep predator populations intact so they can do their work over the long term.