Carabid Ground Beetles

Facts & General Information

The family Carabidae includes over 26,000 species of beetle found throughout North America. Many of the species are common and can annoy residents as occasional or regular invaders. Common ground beetle species found in the home include the black ground beetle and the caterpillar hunter beetle.

Appearance & Identification

What do carabid ground beetles look like?
Ground beetles vary in size by species, with the smallest measuring around 1/16 of an inch and the largest averaging around an inch in length. The insects feature hard exoskeletons and flat, elongated bodies. The body consists of a head, thorax, and abdomen, with the thorax usually being a bit wider than the head and the abdomen wider than the thorax. The head includes long, thread-like antennae and pincer-like mandibles. Hard, ridged wing covers rest atop the abdomen to conceal the wings underneath. Though equipped with wings, most ground beetles are hesitant or unable to fly. Relative to other beetle families, Carabidae have long legs, which give the insects the ability to run quickly and prove advantageous for catching prey. Most ground beetles appear black in color or exhibit dark, earthy tones. Unlike typical ground beetles, the caterpillar hunter has bright, metallic green wing covers with red highlighting the margins. The sides of the insect’s head, thorax, and legs appear rich violet or dark blue in color.

Habits/Habitat

Ground beetles live in nearly any habitat with temperate weather and commonly thrive in meadows, gardens, woodlands, and crop fields. Mountain, desert, and costal environments can also support ground beetle populations. The ground-dwelling insects usually take harborage under dense ground cover, rocks, and old logs, where they remain during the daylight hours. At night, ground beetles climb trees and shrubs in search of insect prey. Populations boom in the summer and fall months, and large numbers of the insects can be seen flocking to light sources during the evenings. Predators of ground beetles include toads, small snakes, shrews, and birds.

Diet

What do carabid ground beetles eat?
Ground beetles mainly feed on insects, and many of the insects preyed upon are pests themselves. Often beneficial to humans, ground beetles eat caterpillars, grubs, fly maggots, wireworms, ants, aphids, and slugs. The predatory insects can also feed on non-pest insects like other beetles and earthworms. Both adult ground beetles and larvae prey on insects. Many ground beetle species feed on the seeds produced by weeds and serve as important natural controls of weed populations.

Reproduction

Ground beetles undergo a complete metamorphosis, which consists of four stages: egg, larva, pupa, and adult. The egg stage begins when the female searches for a suitable location to lay her eggs. A female typically looks for a protected area away from natural predators and lays eggs in the soil, close to the surface. Once a site is found, the female lays eggs one at a time and can deposit between 30 and 600 eggs in one brood. Eggs hatch after about a week. Larvae live entirely in soil and feed on seeds and soil-dwelling insects. The developing beetles overwinter during the larval stage and resume development when temperatures rise. After several instars, larvae pupate in the soil. Upon completing the pupal stage, adult ground beetles emerge from the soil to search for food sources aboveground. From egg to adulthood, the entire development process usually takes about a year, and carabid beetles usually produce one generation annually. After reaching maturity, most ground beetles live about two to three years.

Problems Caused by Carabid Ground Beetles

Although ground beetles can help control weed growth and populations of other pests, the insects can be troublesome to humans. When populations swell in the summer and fall, the pests can be an annoyance both outside and inside the home. The sight of ground beetles in or around the home may cause alarm to residents, especially if beetles appear en masse. Large-sized carabid beetles, like the one-inch long caterpillar beetle, may particularly disturb inhabitants. The caterpillar beetle also emits a foul odor if agitated, which can further bother residents.

Signs of Infestation

Considered regular invaders, black ground beetles represent the most common beetles found in the home. Finding numerous black, half-inch long beetles inside will indicate a black ground beetle infestation. When living in the home, the pests can usually be found in dark, undisturbed areas such as basements and typically hide underneath clutter. Most other ground beetle species serve as perimeter pests and occasional invaders. Numerous carabid beetles crowding around outdoor light sources can alert homeowners to a potential infestation, since the insects may accidentally come inside in search of food. Ground beetles cannot live for extended periods indoors, and finding the dead bodies of the insects can serve as a sign of infestation. In the absence of soil, ground beetles cannot breed indoors (must lay eggs into soil).

Prevention

Ground beetle infestations usually begin when populations thrive outdoors. Homeowners should begin the prevention process outside by eliminating sources of harborage around the home. Removing leaf litter and cleaning up heavy ground cover will reduce the number of places carabid beetles can live and breed near the home. Piles of lumber, bricks, and other debris may also support ground beetle breeding and should be removed or at least kept far away from the structure. Additionally, homeowners want to keep exterior lights off in evenings during times when populations are abundant because light can draw the pests toward the home. Replacing outdoor lights with bulbs that emit less attractive light to insects can also reduce chances of infestation.

After taking outdoor precautions, homeowners want to keep the invaders out of a structure by sealing up any foundation cracks that may provide entry into the home. Gaps around windows and doors may also allow the insects to come in. Proper weather sealing around these openings proves invaluable to keeping ground beetles as well as other pests out. Since carabid beetles prey on insects, keeping the home free of other insects will discourage the predatory pests from entering.