What Do Predacious Ground Beetles Look Like?
Identification. Also called carabids, predacious ground beetles belong to the family Carabidae. There are more than 2000 species in North America alone. The size and color vary depending on the species, but range from 1/8”-1-1/4” long and are primarily brown or black.
Since it is not the scope of this article to identify the entirety of the species list but rather demonstrate the family’s usefulness as a beneficial garden addition, here are a few examples of ground beetles commonly seen in the US.
Caterpillar Hunter. The Calosoma scrutator averages 1”-1-3/4” long and is brilliant metallic green with a blue thorax.
Common Black Ground Beetle. The Pterostichus spp. averages ½”-5/8” long, is shiny black, and has deep, vertical grooves running down the wing covers.
European Ground Beetle. The Carabus nemoralis is one of the larger ground beetles at an inch long. They are metallic purple and coppery in color. The forewings have three rows of dimples along the ridges. It is most commonly found in the northern US though its range is expanding.
Granulated Carabid. The Carabus granulatus averages 5/8”-1” long is dull and brassy looking with a greenish luster.
Green Pubescent Ground Beetle. The Chlaenius spp. averages 5/8” long has a bright green surface, black underside, and brown legs.
How Long Do Ground Beetles Live?
Ground beetle larva can take a full year to develop. Adult ground beetles can live two to four years.
How Are Predacious Ground Beetles Beneficial?
The predacious ground beetle is considered an important biological control agent in agroecosystems. What they eat varies slightly between species, but both the larvae and adult of most eat ants, aphids, caterpillars, cutworms, grubs, maggots, slugs, small snails, and wireworms. They can consume up to their body weight in food every day.
Of additional interest is the fact that some species feed on the seeds of noxious weeds such as common ragweed, giant foxtail, and common lambsquarter. Some experts believe that their value as weed seed predators is underestimated and that they could alter the plant species composition in a given area.
Preserving This Species
Predacious ground beetles, like many other beneficial insects, are susceptible to pesticide use and are often its unintentional victims. A better choice would be an organic pesticides such as Bacillus thuringiensis (Bt), a naturally occurring bacterial disease of insects, which beetles are not susceptible to. Bt is effective against many garden pests including caterpillars and fly larvae such as mosquitoes.