Predaceous Ground Beetles

Predaceous ground beetles are a large family of beneficial insects that live in the soil.

You may see them scurrying across the ground, but mostly these members of Carabidae stay hidden in darkness. There are over 2,500 species of predaceous ground beetles in North America. They are mostly nocturnal and tend to hide under leaf litter and in the soil, though some species are attracted to lights at night.

Caterpillar killer, ’Calosoma sycophanta’ (Calwer’s Käferbuch, Table 4, Picture 9) Public Domain

Predaceous ground beetle description

Predaceous ground beetles are medium to large (1/3 to 2/3 inches long), shiny black or reddish beetles with long legs. Some species have brilliant coloration, and the shape can vary considerably. They have long, antenna with 11 segments and no knobs (clubs) at the end. The abdomen is large and rectangular, with a narrow thorax.

​While they can fly, they mostly prefer to run, which they do very quickly. Predaceous ground beetles look a lot like plant-eating darkling beetles. To tell them apart, you need to look closely enough to see if the second segment of the hind leg (trochanter), found between the coxa and femur, is enlarged. If it is, you have a predaceous ground beetle. Also, the antennae of predaceous ground beetles are attached just below a distinct ridge on the sides of the head.

‘Pterostichus nigra’ (APictche) CC BY-SA 4.0

Predaceous ground beetle life cycle

Eggs are laid in moist soil. When they hatch, larvae that look similar to earwigs emerge. These larvae feed voraciously on slugs and snails, and many bothersome soil dwelling insect larvae and pupa. These pest insects include masked chafers, caterpillars, grubs, tussock moth and gypsy moth larvae, other beetles, and maggots.

Predaceous ground beetle larva (AJC1) CC BY-SA 2.0

Earwig (Beverly Buckley) Pixabay

​While predaceous ground beetles will occasionally eat seeds and organic litter, they prefer meat to vegetables. In fact, adult Calosoma sycophanta (affectionately known as caterpillar killers) eat several hundred caterpillars in their 2 to 4 year lifespan, and their larvae eat up to 50 caterpillars before transforming into adults! While not exactly predaceous, Lebia grandis loves to feed on potato beetle eggs and larvae.

So, the next time you see a black beetle running across the patio, look for fat legs and eyebrow ridges before squashing it!