It’s more challenging to find insects this time of year, but this month at least, it made the victories feel that much more thrilling. This column spotlights a ground beetle in the Scaphinotus genus–a snail-eating beetle.
I’ve found myself turning over rocks and logs lately, and beneath a downed branch under a white oak I was rewarded with this purple-shimmering, rather large and handsome beetle. A few of the things I’ve since learned about it made me wish I’d spent more time with it.
You may have been struck by the “snail-eating” part of its name. Their diet has shaped not only their body parts, but also their life cycle and preferred habitat. Scaphinotus beetles have narrow heads and, if you look close at the complicated circus of mouthparts, you’ll see a toothed jaw that’s a bit golden and four palps with scoops on the end of them. According to one source (noted below), the scoops are equipped with sensors at the tips that detect snails. The narrow head helps it enter a snail shell, and the jaws … they do what jaws do. The same article says, “When a snail is captured, they shake it around like a puppy with a slipper.” Wouldn’t that be an awesome sight!
Snail-eating beetles are mostly nocturnal and live in moist places. Like many ground beetles, they don’t fly because of reduced wings and fused wing covers. To compensate, they have long legs and can cover ground quickly. Scaphinotus beetles may take a long siesta, or go into diapause, in dry summer months when they’re less likely to find their preferred food. From the records on BugGuide, I’m guessing there are fewer adults alive from December to March, but one source I found says both larvae and adults can survive the winter.
There’s one more evocative detail about these beetles: I read in a few places that all species in this genus emit a sickly sweet odor, one saying it smells like raspberry jam. Researchers say this is a defensive scent, so I guess their predators aren’t fans of PB and J.
Great description of hunting behavior from the Carnegie Museum of Pittsburgh: https://carnegiemnh.org/hillbilly-gourmets-snail-eaters-of-the-yew-mountains/. Accessed 12/18/20.
Well-done article with some solid basic information: https://crawford.tardigrade.net/bugs/BugofMonth29.html. Accessed 12/18/20.