I had hoped to get some garden clean-up done this weekend, but it snowed a bit:
Given the winter weather, you might wonder how I could be doing another insect story, but right now I’m hosting an extra house guest. The beetle first showed up wandering the hallway at school, near the back doorway. Carabids are generally hunters, and many of them are beneficial to us because they eat pest insects. Chances are you’ve seen the ordinary sort of brown-legged, large black ground beetle running across the sidewalk in search of prey, or maybe hanging around your porch light at night.
Carabids can be distinguished by a couple of characteristics: firstly, the pronotum (the dorsal plate of the prothorax, meaning the section on the back of the beetle that’s between the head and body) is wider than the head but narrower than the rest of the body, and secondly, on the third (hind) legs the trocanter makes a rather distinctive lobe between the femur and coxa (diagram). Like many sorts of beetles, the elytra are striated, which is a fancy way of saying that the wing-covers are grooved.
There’s certainly no lack of beetles in the world; with about 40% of the species, Coleoptera is the largest of the insect orders. But once you get to know my guest, you won’t forget it — this is one smashingly gorgeous hexapod!
The Caterpillar Hunter (Coleoptera: Carabidae, Calosoma scrutator) also has another common name, the much more exciting Fiery Searcher.
Description: a nearly 3 cm (1.25″) long beetle, with shiny dark blue legs, black antennae, a metallic navy pronotum rimmed in orange, and grooved metallic green elytra rimmed in copper-red. The beetle is photographed on graph paper, with an off-white caterpillar clenched in it’s pincers. (I put the graph paper in its cage just for better photography, because despite its flashy coloring, the predator is not very noticeable against dark soil.)
At school, I carefully scooped up the beetle and popped it into a cage for the students to view safely, because those mandibles can give a nasty bite. I also bought some “wax worms” (a type of moth caterpillar) at the pet store to feed it, but since the beetle is mostly nocturnal, it proved to be a rather boring classroom pet as it spent most of the days snoozing in a crevice between a small rock and the soil substrate in the cage. (Well, I assumed it was asleep but it’s hard to tell with animals that lack eyelids; it was alive but not moving.)
Ground beetles are so named because that’s where they live; they like the cool damp spots, and hang out underneath rocks and bark and other debrís. Females lay individual eggs in the soil, where the larvae will return to pupate. But being caterpillar hunters, they are also found climbing trees in search of gypsy moth or tent caterpillars, especially during the spring.
After a couple of uneventful (read, “boring”) weeks, I took it home. Adults can live two or three years; I’ve no idea how old this one is, but it might be here some time. Today I waggled a waxworm right in front of its jaws, which prompted a quick response. My eldest described it as a “dedicated feeder”, as the beetle spent quite a while steadily consuming the caterpillar that was nearly as long as it was. It was, I noted, also a fastidious eater, as it only ate the insides of the moth larva, finally abandoning the rumpled exoskeleton, much in the way that we leave shrimp shells on our plates. It then wandered over to the side of the cage by the desk lamp, and sat in the warmth to better digest its dinner.
Like the rest of the Thanksgiving diners, my house guest is currently snoozing off its repast.