Field Notes: What’s Lurking Under That Log?

(With this entry, Rural Action’s Environmental Education team launches Field Notes, an occasional series that takes readers into local forests to learn about our natural world. This installment is by Joe Brehm, Environmental Education Director.)

Carabus vinctus, the Round Worm and Slug Hunter Beetle

On a team walk through the “pin oak swamp” near Payne’s Crossing in the Wayne National Forest, I roll over a small log. Exposed all of a sudden to the morning sun, a large beetle shuffles for cover, but I manage to take a decent photo before it strolls beneath ample leaf litter and out of sight. I post the photo to iNaturalist and a beetle lover somewhere quickly identifies the beetle as belonging to the genus Carabus (family Carabidae) and another blessed biophile identifies the beetle as Carabus vinctus, the Round Worm and Slug Hunter Beetle. Quite a common name. Though Arthur V. Evan’s Beetles of Eastern North America does not mention this species as rare, this is the first iNaturalist observation of Carabus vinctus in Ohio. Evan notes: “adults active spring through fall, found in wet deciduous woodlands, often near water under leaf litter, bark, logs; also attracted to light and banana bait.” There are beetles such as C. vinctus who specialize in eating slugs and worms; other species hunt caterpillars or even other beetle species’ larvae.

A “hitchhiker” hangs on to the much larger Oil Beetle, where it grabs some of the poison the larger beetle uses for protection so it can protect itself.

If the girth of Beetles of Eastern North America is any indicator, beetles are a big part of biodiversity in our region. They are easy to overlook, however, as many are nocturnal, spend most of their lives living under logs and leaves, or even chew through rotten logs to feed on slime molds in their amoeba stage. One genus that is impossible to overlook, however, is Meloe, commonly known as the Oil Beetles. Large and in charge, they roam the forest floor in broad daylight, their metallic blue plump abdomens on display and visible even through an impressive carpet of spring wildflowers. It seems as though I see one of these every spring, and only one. Two of the last three carried “hitchikers” along, a much smaller beetle species attached to the big Meloe like an eel on a fish. Why, you may ask? Because Oil Beetles have a poisonous chemical known as cantharidin that oozes from their joins when disturbed that causes blistering and painful swelling. The smaller beetle, almost certainly in the genus Pedilus, is stealing some of this chemical for its own protection, which is passed off to mates during copulation and even to their baby beetles. What a surprise that toxins are a hot commodity among beetle species, and that they exchange it (albeit unwillingly) beneath our phlox and morel seeking noses this time of year.

To date, 475 volunteers have contributed close to 16,000 observations like this one of Carabus vinctus via iNaturalist to our “bioblitz” of the WNF’s Athens Unit, documenting roughly 3,400 species of plants, insects, fungi, mammals, birds, and more. You can join us by following instructions here.

Happy exploring, and let us know what you find under logs near you.