With the onset of winter it’s been a little while since Dan brought me any interesting nature discoveries, but a couple of days ago he walked into my study and set something down on my desk. It clicked as it landed lightly on the wooden surface. “Two of these have been flying around my lights all morning,” he said. Bugs seem to like Dan; I rarely have anything flying around my lights. The odd ladybug, perhaps.
In this case the pestering creature was a stink bug. Sometimes also called shield bugs for their medieval-shield shape, they have the distinctive (and memorable) ability to produce foul-smelling secretions when threatened or disturbed. The idea is that the smell will put off potential predators; since most birds have a very poor sense of smell, presumably the secretion also tastes bad. If you catch a stink bug in a bad mood, you’ll soon know it. Fortunately, this one seemed to be pretty calm.
Using my Kaufman Field Guide to Insects I narrowed the genus of this individual down to Brochymena (rough stink bugs, I think so-called for the toothed edges to the pronotum, the section right behind the head), and then went onto BugGuide to figure out the species. I’m pretty sure this is a Four-humped Stink Bug, B. quadripustulata (“four pustules”?), which is one of the more common and widespread members of this genus. The KGI indicates that adults of some Brochymena species hibernate as adults beneath bark, so I’m wondering if these two came in with the firewood.
I found it interesting how much red the bug had on it, when I looked at the photos. To my naked eye it seemed fairly uniformly brown, with some darker Vs at the shoulders and around the bottom of the scutellum (the bit in the middle of the back that appears as a pale U in the first photo, and which didn’t stand out as pale to my eye). It amazes me how much detail cameras reveal in these smaller subjects, and it’s one of the reasons I enjoy photographing moths and other insects so much. (Incidentally, the random little pale dashes, such as the one on his head, are moth scales. I had him in one of my moth jars until I got my camera equipment set up.)
Although some of the 250 species in family Pentatomidae are hunters of other arthropods, most feed on the sap of plants. Some can be serious crop pests. They stab the plant with their long, thin proboscis and use it like a straw to suck the sap out. This doesn’t usually kill the plant (except in cases of bad infestations) but because a scar will form where the plant was pierced it can create deformities and blemishes – a problem for farmers trying to sell their produce for human consumption since we humans are so picky about the aesthetics of our produce. Sometimes it will destroy seeds, which can be problematic for grain crops or things like corn, where the seed needs to be whole to be useful. When not in use, the proboscis is tucked firmly against their underside. You can see it here as a thin line going from the head down between the legs.
The other interesting thing you can see on its underside is the scent gland that produces the stink. It’s just a small divot in the side of the thorax, dorsal to the middle leg (ordinarily, when the bug is upright, it would be right above the leg, but in this photo it’s right below). A close-up of the gland is below, indicated with an arrow. Not the best quality, but he was squirming a lot, rowing his legs and pushing against the stone to try to flip himself upright. He wasn’t having a lot of success, and as soon as I got the photo I turned him over again. (For a better-quality photo, check out this one on BugGuide.)