Last Thursday, after I re-found the blister beetles for my brother Steve, we walked back through the flowering oak woods. It was a sunny day, and the woods were filled with butterflies.
Juvenal’s duskywing (Erynnis juvenalis) – not to be confused with the very similar Horace’s duskywing, which emerges later on in the summer – almost disappears when it lands on the forest floor. It’s strongly associated with dry, upland oak habitat, emerging from the chrysalis just as the oaks are bursting their buds. We were probably seeing males patrolling for females; each seemed to circle a fairly small area.
After mating, the female duskywing will lay her eggs singly on scattered oak leaves. The caterpillar will munch away on its oak leaf in splendid isolation – unlike, say, tent caterpillars – and will roll the leaf around itself like a sleeping bag whenever it rests. To each his own method of camping out, I guess. The adults feed on nectar from a number of species, including blueberry, which is the main ground cover here. They are said to sleep “with wings folded rooflike over the back, in the manner of a moth.”
A brilliant green six-spotted tiger beetle lands on the trail in front of me, and I go into the photographer’s crouch (see the photo in Friday’s post). This is quite possibly the most-photographed beetle species in the world, Steve says. He adds that when he was a kid, he used to have to go to the Scotia Barrens near State College to find any tiger beetles, but thirty years later, Cicindela sexguttata has become a common resident here on the mountain. I wonder if that might not be due to an increase in available prey. As a forest matures, it becomes structurally more diverse, with more forest openings and fallen woody debris, and insect numbers and diversity increase correspondingly.
Tiger beetles are famous for their ferocity, but there’s more to them than that. After six-spotted tiger beetles mate, the male rides around on the female’s back for a while to make sure nobody else gets a chance at her. Or at least, that’s how the scientists explain it. I suppose it might just be a prolonged afterglow.
We pass a fallen scarlet oak log, and Steve gets his knife out. “Oak logs like this are a gold mine – you never know what you’re going to find,” he says happily as he begins ripping off pieces of bark. Grubs and spiders go scurrying.
Daylight crashes rudely in on a scarab beetle larva, which squirms and burrows deeper into the rot as I snap its picture. It somehow manages to be both beautiful and repulsive at the same time.
A brilliant green halictid bee pauses in front of a slug. Perhaps we’ve just interrupted something important; we’ll never know. “Halictid” means “salt-loving,” Steve informs me. “There are a huge number of species, including those little sweat bees that like to sting after they’re finished drinking your sweat. But most of them are harmless, like this one.”
We spot two tiny snails, barely a millimeter across. Snails were one of the earliest animals to colonize land, and they’ve been doing quite well in the 350 million years since. By some estimates, one acre of moist temperate woods might harbor 1.5 million snails; a montane forest in Panama was estimated to hold 7.5 million snails. I guess if you know what you’re doing, you’d never have to go hungry. But one can only eat so much escargot.
Our most spectacular find was an orange-red larva of an elaterid, or click beetle. Some click beetle larvae – smaller than this one – are known as wireworms, and arouse fear and loathing in many gardeners. But adult click beetles are every kid’s favorite insect, especially the huge eyed elators with false eye spots on the back of the thorax. Click beetles are so called because of their unique, two-step defensive strategy. First, they roll over on their backs and play possum, without the grin. If that doesn’t work and the predator – or a finger – actually makes contact, they flex the head and thorax backward, then suddenly straighten out with an audible click that fires their bodies several inches into the air.
“Not too much is known about beetle larvae in general – they’ve hardly been studied at all,” Steve notes. Most of what we think we know is based on what we can most easily see, so even for relatively charismatic insect species like tiger beetles and click beetles, we have few notions about their behavior during the 90-some percent of their lives spent in the juvenile form.
The limitations of our current method of investigation – rapid roof removal – for learning anything about insect behavior are obvious. In one crevasse, we surprise a pair of cave crickets, side by side but not mating. They sweep their amazingly long and sensitive antennae back and forth like a blind person feeling for the curb. I can’t resist quoting from a Japanese website:
Many of cave crickets have the round back, it has the form of having been the thickset, and there is no wing. Hind legs and an antenna are very long and detect existence of a surrounding situation and a foreign enemy in darkness by shaking and moving this antenna from back to a front. In the color of the body, it is brown, an eye degenerates, and, as for gray or the thing which was adapted for the cave, the body is soft. It lives by preference under the damp places in a cave etc., and a stone and the fallen tree.
Cave crickets are omnivorous, and can go for a long time without food. To stave off starvation, they will eat their own legs, one by one.
“Oak logs are the best,” Steve says as we make our way down to the stream. “You won’t find anywhere near the same level of biodiversity under the bark of a pine log, for example.” I feel another piece of the ecological puzzle snapping into place. I knew that oaks were keystone species in the Appalachian forest, but I had always thought in terms of acorns and den trees – the scale I’m familiar with. From what Steve is saying, it sounds as if, prior to the death of an oak, its contribution to the food web has barely begun. And doubtless a wood so prized by invertebrates must furnish more than its fair share of nutrients for soil microorganisms, as well.
We pass a beech log, and Steve pulls back a strip of bark to show me a smooth, unpopulated surface. But then he spots an old bracket fungus, A.K.A. artist’s conk. “This is where you find stuff on a beech log,” he says. He pulls it off and shows me the underside, which is pocked with small craters.
“These are the exit holes of Bolitotherus cornutus, whose name translates as ‘horned fungus beast’! Here, let’s find one so you can get a picture of it.” He starts digging into the rotten conk with his fingers. “A-ha!”
“That’s an insect?”
“Yup. I’ll put it on my hand so you can get a better look.”
“It’s a type of tenebrionid, or darkling beetle,” Steve explains. Most tenebrionids are desert dwellers, but this species has adapted to life inside rotten shelf fungi. It isn’t so much camouflaged as thoroughly imbued with its environment, which is caked between the ridges of blunt, tuber-shaped projections on its back. A much better picture of a clean female fungus beast can be seen here. The accompanying photo of a male shows the horns for which it was named. It looks like nothing so much as a miniature Triceratops.
According an abstract of a paper I found online, B. cornutus has well-developed wings, but has never been observed to actually use them, preferring, apparently, to walk. In a mark-and-recapture study, a few individuals were found at distances greater than those predicted from observations of its regular style of locomotion. Perhaps they did short sprints when no one was watching.