The Secret Lives of Insects #6

Ground Beetles: Midnight Marauders

By Judy Ferris, ACLT Guest Blogger

Who would imagine that a beetle with a face like this would be a gardener’s best friend? Your first instinct upon seeing this critter may be to stomp it before it hurts someone. But wait a minute!

Ladybugs, move over! It’s time we discovered the nocturnal guardians of our gardens. Night after night, unnoticed and unloved, humble Ground Beetles toil to rid our gardens of pests. They are, in fact, some of the most beneficial insects in our gardens. Since Ground Beetles are nocturnal, however, we seldom notice them. By day they hide in grasses, or beneath rocks, logs, or mulch in order to stay cool and moist. As the sun sets in the evening, however, adult and larval Ground Beetles begin to hunt. They churn below the ground, skitter atop the soil, climb plants, and even ascend trees as they forage. What’s on the menu? It’s an all-you-can-eat buffet at the Insect Smorgasbord! Ground Beetles are prodigious consumers of a wide variety of insect pests that we would happily remove from our gardens; mites, snails, slugs, caterpillars, earwigs, cutworms, vine borers, aphids, and many other insects.

Ground Beetles are members of the Carabid family. With over 2000 Carabid species in North America alone, Ground Beetles are a common insect. They range in size from 1/8 to 1 1/2 inches long. If we examine this beetle closely, we can see that it is configured to be the perfect nocturnal predator. Ground Beetles rarely fly. Instead, they use their long, agile legs to hunt and pursue prey in the darkness. Most Ground Beetles are dark and shiny. They have large eyes as befits a night hunter. Those take-no-prisoners jaws are perfect for processing all kinds of prey; from slimy slugs, to gummy-bear cutworms, to crispy-critter ants. Some Ground Beetle jaws are even designed to puncture the shells of snails.

To watch those intimidating jaws in action, check out the video below Ground Beetle vs Corn Ear Worm. Warning! The video is best not viewed immediately before or after a meal!

An adult Ground beetle can eat its own body weight in prey insects nightly. Beetle larvae are equally voracious. A single beetle larva can eat more than 50 caterpillars during the course of its development.

As a family, Ground Beetles are the master chemists of the insect world. Thanks to chemistry, many Ground Beetle species can emit a lingering noxious smell from their rear ends to discourage predators. One branch of the Carabid family, Bombardier Beetles, has elevated this talent to an art form.

Behold the Bombardier Beetle! When threatened, this elegant little beetle can aim and shoot a hot, chemical cocktail from its butt to a distance of several times its body length. The chemical blast is accompanied by smoke as well as an audible pop as the chemicals detonate. How does the beetle do this? According to researchers at Penn State University, ground beetles have a unique gland system which allows them to store toxic chemicals such as formic acid, concentrated hydrogen peroxide, and phenolics in the tip of their abdomen. When needed, the chemicals are squeezed out of the glands and moved into firing position near the anus. There, the chemicals react with special enzymes to ‘fire’ (oxidize) the chemicals; releasing heat and gaseous oxygen that shoots the boiling hot (212 degrees!) material out of the Bombardier’s butt (Marshall 2006).

For a fascinating 4-minute video from the BBC on chemical warfare in the insect world, click on the link below. You’ll see Bombardier Beetles in action at the end of the video. Impressive!

In case you are wondering… Yes, a blast from the Bombardier Beetle can burn your fingers and stain your hands. Thus, if you are lucky enough to find a Bombardier Beetle, it’s best not to handle it. Personally, however, I’m delighted to know that a squadron of Ground Beetle caretakers patrols my gardens nightly, apprehending and puncturing pests! When I do happen upon them by day, Ground Beetles are not threatening, but are instead, welcome residents. May they live long and have many babies!

To attract beneficial ground beetles to your garden, create a simple beetle refuge as described below by Landscape Designer Darcy Larum.

“Build a small raised garden bed at least 2 feet wide and 4 feet long. Plant native perennials and grasses in this bed and give it a good layer of mulch. Add some large rocks or logs for décor and ground beetle hideouts. Let debris build up enough to encourage ground beetle eggs, but not too much to snuff out plants. Do not mow, till, or spray pesticides in this area.”

Additional information on Beetle Banks: https://savvygardening.com/build-a-beetle-bank-or-bump/

Ground Beetles: Midnight Marauders

Read Other Posts In This Series