Beneficial Ground Beetles

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Photo by Fotolia/Gudellaphoto
These ground beetles feed on garden pests, even climbing trees to get to tent caterpillars.

These big bugs were obvious inside our garden many years
before we had children, but the youngsters, being close to
the ground, forced us to slow down and pay attention to
them. The bugs were given names, professions and lifestyles
(lucky for them, they were too small to dress in doll
clothes), and their habits were studied closely, too.

The tremendous numbers of small insect eggs laid in
temperate and tropical habitats make it imperative that a
number of slightly larger creatures be available as diners,
to help control this mania for multiplication. The ground
beetles, or Carabidae, are just one of the largely
predacious insect families designed for the job. They
number at least 2,500 species in North America, and both
adults and larvae are predacious. A majority are dark in
color, and some have a distinctive shiny or metallic sheen.

One of the beauties of diversity lies in the seemingly
redundant layers of organisms that almost, but don’t quite,
duplicate one another’s purpose. Within the ground beetle
family, a few eat seeds, a few concentrate near water, and
some readily climb trees and consume arboreal insects,
including aphids and forest tent caterpillars. One species
is commonly found in beaver lodges!

But most are terrestrial predators. Of those, some
specialize in eating a certain type of insect adult or
larvae, but most are not what you’d call discriminating
diners. Most of the carabids are nocturnal, and they can
move quickly on the ground. Many are big relative to their
wing size, which makes them poor flyers; you’ll nearly
always see them walking.

The head is noticeably smaller than the thorax, too, with
very thin, threadlike antennae. This beetle’s other
noticeable feature is a set of parallel lines on the front
wings that serve as the cover for the hind (flight) wings
and abdomen. If you look closely, you will see on some
species, these lines are actually rows of small dots or
pits. Also, some species can emit a strong, foul odor if
handled — we found this out firsthand.

Many garden pests are ground beetle food: cutworms, codling moth
larvae, tent caterpillars, slugs, snails and cankerworms to
name a few. Some beneficial insects will fall prey to them,
too.

If you are using mulches in your garden, you are providing
good carabid habitat. Leaf litter and such are good places
for ground beetles to look for food and to hide themselves
from their own predators. Many hibernate in litter as well.
Most carabids pass through one full generation in a year,
but the process takes longer in colder climates. If you are
in need of a half-hour dose of sunlight, consider finding a
friendly ground beetle and saying ‘hello.’