Though most people cringe at the sight of an insect, there are countless species of beneficial insects. One such group of insects is referred to as natural enemies. These are insects that prey upon other insects that frequently cause damage in the garden or landscape. Natural enemies can be divided into two main categories: predators and parasitoids.
Predatory insects feed on other insects. There are many different species with various feeding habits. Some predators eat their prey whole while others suck out the bodily fluids of their prey. Many predatory insects are skilled fliers and/or runners which aids in catching prey. Some predators use intricate crypsis (camouflage) that allows them to ambush their prey. Others feed on slow, sedentary insect species; therefore, they do not require speed nor stealth.
Lady beetles (Family: Coccinellidae), often called ladybugs, are among the most recognizable insects and are very common and voracious predators of aphids. Lady beetles eat aphids whole and may gobble down as many as 5,000 throughout the course of their life. The adults and larvae are predacious. Lady beetles also feed on caterpillars, moth eggs, scales, mites, and they may also be cannibalistic if prey is scarce.
Ground beetles and tiger beetles (Family: Carabidae) are common in almost every environment and come in a variety of shapes, colors, and sizes. Generally, they have large eyes, long legs, and large, powerful jaws for grabbing prey. Ground beetle are constantly on the move, searching for prey by sight, though some species detect prey by scent. Ground beetles and tiger beetles feed on aphids, caterpillars, other beetle larvae, fly larvae, mites, springtails, slugs, and even small weed seed. The adults and larvae are predacious, but larvae live in the soil and have a smaller search range. Ground beetles can consume up to their body weight each day.
Assassin bugs and ambush bugs (Family: Reduviidae) are true bugs, meaning they have piercing/sucking mouthparts. They feed by inserting their proboscis (straw-like mouthpart) into their prey, injecting digestive enzymes, then sucking out the bodily fluids. This is another extremely diverse group of beneficial insects. Assassin bugs can kill prey that is significantly larger than they are and are common predators of caterpillars, aphids, beetles, and others. Ambush bugs use crypsis (camouflage) to hide on flowers, where they lie in wait for their prey. When an unsuspecting victim gets too close, they have raptorial (praying mantid-like) front legs, specialized for grabbing prey. Ambush bugs feed on flower foraging insects, including small beetles, flies, bees, and wasps. Adults and nymphs in this family are predacious.
Green lacewings (Family: Chrysopidae) get their name from their lacy-looking wings. Adults feed on nectar, pollen, and honeydew and are commonly observed flying around lights after dark. Eggs are laid at night on the tip of a thin, hair-like stalk about a half inch long. This keeps the eggs up and away from predators, such as sibling lacewings. The larvae are wingless; therefore, they crawl around on plant leaves in order to search for prey. They are mainly predators of aphids, but will also eat small caterpillars or beetle larvae. Green lacewing larvae can eat between 100 and 150 aphids in their lifetime.
Syrphid flies (Family: Syrphidae), also called hoverflies, are commonly observed hovering around flowers, feeding on nectar and pollen all while contributing to pollination. Syrphid fly larvae; however, are voracious predators of aphids, scales, thrips, and small caterpillars. Adults frequently lay their eggs among or near aphid colonies to ensure the larvae have plenty to eat. Once the blind and legless larvae hatch, they go to work crawling around and sucking the bodily fluids out of their prey. As they visit flowers, adult syrphid flies are often mistaken for bees or wasps. An easy way to distinguish them is to count their wings, assuming they sit still long enough. Syrphid flies have two wings whereas bees and wasps have four.
Robber flies (Family: Asilidae) are a highly diverse family of flies. They typically hunt for prey from a perch overlooking sunny, open areas. Once located, robber flies grab their prey in midair and inject it with neurotoxic saliva which rapidly immobilizes it. The prey is then carried back to the perch to be eaten. Enzymes in the lethal injection help digest the prey’s bodily fluids, making it easier for the fly to consume. Males hunt for a mate in a similar fashion, minus the lethal injection. Robber flies prey mostly on flying insects such as other flies, beetles, true bugs, butterflies, bees, and wasps. Larvae develop in the soil, but are also predacious, feeding on insect eggs, other larvae, and soft bodied, soil dwelling insects.
Dragonflies are one of the oldest groups of winged insects in the world. There are over 5000 species of dragonflies worldwide. The largest family, Libellulidae, includes over 100 species in North America alone. Dragonflies are strong, agile fliers and have keen eyesight. They catch their prey in the air and feed on almost any insect smaller than they are, especially midges, mosquitos, butterflies, and damselflies. Adult females lay eggs by flying low over the surface of water and tapping the tail end of their abdomen on the water, shaking eggs out as they fly. Eggs may also be laid on aquatic vegetation. Larvae develop in the water and are predacious on other aquatic insects. Once mature, they climb out of the water to pupate and take to the skies.
Praying Mantids (Family: Mantodea) are easily recognized by their raptorial front legs that give them the praying appearance. Crypsis helps them blend into their surroundings as they ambush or stalk prey. Once within reach, they grab their prey with their front legs in a lightning fast motion and bite the victim’s neck to immobilize it. Mantids will eat nearly anything they can catch including flies, moths, crickets, grasshoppers, and even small vertebrates. Females lay eggs in a dense, foamy case called an ootheca, which contain up to 400 eggs. When the eggs hatch the nymphs may cannibalize each other if no other food is available.
The family Vespidae includes many common wasps such as paper wasps, yellow jackets, potter wasps, and hornets. Members of this group can be solitary or eusocial. Eusocial species build nests out of papery material made up of chewed wood or leaves. Most species are opportunistic feeders, whose diets consist of nectar, honeydew, or other insects such as caterpillars, aphids, midges, leaf miners, and spiders. Workers frequently carry dismembered prey back to the nests to feed developing larvae. The larvae of some solitary species exhibit ectoparasitic (live and develop outside of their host) feeding behavior.
Parasitoids are insects that develop at the expense of a host insect, eventually killing it. Parasitoids live and develop either within their host (endoparasitic) or outside of it (ectoparasitic). In most endoparasitic species, adult parasitoids oviposit (lay or insert) an egg into the body of the host, where it grows while gaining nourishment from within the host’s body. The host dies after the parasitoid emerges to pupate. In ectoparasitic species, adult parasitoids paralyze the host and oviposit an egg on the outside of the host’s body. The host is then taken back to a nest where the larvae can develop outside of the host’s body without being disturbed.
Ichneumonid wasps (Family: Ichneumonidae) differ from paper wasps and hornets in that they use their stinger to oviposit eggs into a host, rather than sting for defense. When the egg hatches, the larva feeds on the innards of its host before eventually boring its way out of the host to pupate. Common host insects include caterpillars and the larvae or pupae of beetles, flies, and other wasps. Most ichneumonids are solitary, meaning a single larva develops and matures within a host. Species vary greatly from one another, though most are slender wasps with long ovipositors that are often longer than their bodies. This is the largest wasp family in North America with over 3,300 species.
Braconid wasps (Family: Braconidae) are generally smaller than ichneumonids and often go unnoticed. Females oviposit eggs into host insects similar to ichneumonids and can be solitary or gregarious (many eggs deposited into a host). The larvae of some species remain attached to their host after exiting to pupate. This is commonly observed on large caterpillars, which may have a few dozen pupae attached to their backs. Other common hosts include aphids, beetles, flies, ants, and bugs. Braconid species vary greatly in habit and may parasitize the eggs, larva, pupa, or adult stages of their hosts. Additionally, some species of braconids are ectoparasitic. This is the second largest wasp family in North America with 1,900 species.
Tachinid flies (Family: Tachinidae) are a large family of parasitic flies. Females of most species lay eggs directly on a host insect. When the egg hatches, the larva bores its way into the host’s body to feed internally. In other species, females lay eggs on the surface of a leaf where it may be inadvertently ingested as the host forages. These eggs hatch within the host’s body. Once fully developed, the larvae exit to pupate in a process which usually kills the host. Adults are frequently seen foraging flowers, where they feed on nectar and contribute to pollination.
Sphecid and cabronid wasps (Familys: Sphecidae and Cabronidae) have long legs and thin waists. Common members of these closely related groups include mud daubers, thread-waisted wasps, and cicada killers. Most species nest in the ground, though some, such as the mud dauber, construct nest out of mud well above the ground. Nests are provisioned with insects or spiders that have been stung and paralyzed. Eggs are laid on the prey, which is then fed on as the larvae develop within the nest. Adults can be observed foraging flowers and feeding on nectar.