Common Black Ground Beetle

An important player on the beneficial insect team

By Scott Creary

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The Commom Black Ground Beetle is a Beneficial Garden Insect.

Pterostichus spp.

In the bug-eat-bug world of beneficial insects, the majority of the players are unknown to us. Such is the case with common black ground beetles (CBGBs). Their unremarkable appearance, nocturnal nature, and reclusive tendencies keep them off most gardeners’ radars until weeding, digging, or some other disturbance brings them out into the open. Don’t be fooled: CBGBs, among the most abundant good bugs, are valuable team players in the organic garden.

These beetles are 1⁄2 inch long and glossy black, possessing a distinct head, thorax, and abdomen with multiple ridges running its length. Females lay eggs underground in late summer, and the nondescript larvae spend the winter there, hunting subterranean insects, temperature permitting. The adults reside in weed patches, brush piles, mulch, or other dark, moist areas, emerging at night to feed on grubs, maggots, and turf-dwelling pests. Though they lack ferocious physiques or demeanors, CBGBs compensate with speed and ingenuity.

CBGBs don’t fly. Rather, they run—or sprint, more fittingly—to catch prey and escape their own predators. They prefer to hunt in relatively sheltered environs under vegetation or thick mulch, only hesitantly venturing into the canopy to nab aphids, caterpillars, and soft-bodied herbivores. However, when foliar predators are on the prowl, many of these same herbivores drop to the ground, falling from the proverbial frying pan and into the fire. Studies show that ground beetles, in tandem with their canopy-hunting counterparts, act synergistically, reducing pest numbers more together than either would individually.

For this reason, what helps one good bug will help another. Planting nectar-producing plants will attract the airborne hunters that drive prey to the soil level, which in turn bolsters food resources for soil-dwelling predators like CBGBs. That said, they also need an escape from daytime heat, so bring on the mulch! Loose, organic mulch provides an ideal refuge for these and other “ground forces.” And for controlling turf pests, consider installing an insectary strip: a patch of flowering weeds, herbs, ornamentals, and taller grasses that will attract predatory insects to your lawn.
 

Originally published in Organic Gardening Magazine, April/May 2014

Illustration: Jack Unruh

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