caterpillars

One of the necessary chores that comes with keeping horses, of course, is having to muck out the stalls. It’s a pleasant sort of physical labour, where you feel you’ve had a good workout and been productive at the same time. If kept on top of every day it’s neither a lot of work nor very time consuming, but can add up quickly if neglected.

It was while I was busy doing this that I noticed today’s subject. I was returning from dumping a wheelbarrow load, my mind on other things (such as wondering how Mom still does this every day, at her age), and so wasn’t paying a lot of attention to bugs or other critters. If this bug had been anywhere else on the maple tree I probably wouldn’t have noticed, but it was at the tip of the very lowest leaf of the branch that hangs over the driveway, pretty much at eye level. And the bug was red and black. Hard to miss.

It was busy laying eggs. Naturally, I didn’t have my camera since I was working in a spot I wasn’t keen on the camera being, so I dashed indoors to grab it and came back to run off a few shots. She was oblivious, focused on the task at hand, I guess, And I was able to manipulate the leaf to pick up the best light (and also to keep it steady and easier to focus on in the light breeze).

When I came back inside and looked it up in my Kaufman guide to insects, it was shown there as a Box Elder Bug, Boisea trivittata. I thought, Elder? What’s it doing on the maple, then? And it wasn’t alone. A few leaves above it was this solitary individual, who seemed to either be lost or looking for a mate as it roamed from leaf to leaf. A few leaves further I noticed a pair copulating (below). I’m not sure if the larger one is the male (as is traditional in many species) or female (since she’s the egg-layer and needs the size to haul them about). They certainly didn’t seem to feel out of place.

Well, it turns out the Box Elder is actually more often called Boxelder, and is not a type of elder at all, but rather a maple, a member of the genus Acer. The Eastern Boxelder Bug, as it’s called on BugGuide.net, is also sometimes known as the Maple Bug, and will lay its eggs on the foliage, seeds or bark of Boxelder and other maple species, and also ashes. So it wasn’t in fact out of place at all. The nymphs, when they hatch, feed on the seeds of the trees, as well as opportunistically on dead insects. The adults primarily feed on the plant’s juices.

Apparently the adults are most often seen in the fall, but are also around in the spring. BugGuide indicates the spring period is primarily May, so what they’re doing out in late June, I don’t know. It could be that the May date applies to a different area than here, since the species is found across most of North America east of the Rockies. Supposedly they can be a house-invader in late fall, as they’re looking for a place to spend the winter, much like ladybugs, but I don’t think I’ve ever noticed them doing that here.

I left the female to it and she finished up laying. When I checked today there were about ten of these small, soft eggs, no bigger than the head of a pin. I don’t really know, but I would guess that the pale crescent you see on one end of the eggs is akin to the yolk of a bird’s egg – the fertilized cells sit on that, and that’s what the developing embryo uses for food.

Edit: Commenter Ted indicates, “The orange crescent you noted on the bug eggs is actually the outline of the operculum, which is the “cap” of the egg – when the nymph hatches, this cap will pop off and out will crawl the nymph. Eggs of most “true” bugs (order Hemiptera) have these opercula, as far as I can tell.” Thanks, Ted!

The branch was surprisingly full of activity for just a little section of tree. While examining the bugs, I happened to notice a light green caterpillar just a few leaves over. I don’t know what species this is, and I couldn’t even tell you if it was a butterfly or a moth, though I’m inclined to think the former. I used to believe that moth caterpillars were hairy and butterfly caterpillars were smooth, but it turns out that either can be either, and so now I know of no reliable way to differentiate the two. The inchworms, though, those little guys with feet at each end, who inch rather than crawl, those guys are moths, as are the really, really fuzzy ones like the Woolly Bears.

I didn’t notice it at the time, but in looking at the photo as I cropped it down, I spotted a white glob at the back of the caterpillar’s head. I’m fairly certain that this is the egg of a parasitic insect, probably a fly. There are a number of species of flies that lay their eggs at the back of the head of caterpillars, where the caterpillar can’t remove it. When the egg hatches, the larva burrows into the caterpillar’s body, and lives there, without killing the host, until it’s ready to emerge (at which point the host usually dies). Some caterpillars, such as tent caterpillars, have evolved a response of rapidly twitching their front end back and forth when they see a fly so that it’s a much harder target to land on.

Also in the area were many of these fuzzy caterpillars. Again, I don’t know what they are, but they were very brightly coloured, and the density and length of the hairs makes me think moths. There were many different instars, or larval stages, of these caterpillars on the branch, from the fairly mature one above, to a middle-aged and even rather young. On a few leaves I spotted the empty, shed skins (below) of caterpillars as they move from one instar to the next.

It’s amazing how much there is to see when you stop to look; if it hadn’t been for that one bug, laying its eggs on the low-hanging leaf, I would have just walked right on by, thinking the branch was empty.

Edit: This post was recently included in the 180th edition of Friday Ark, a weekly blog carnival focusing on animals of all sorts. You can check out the full edition at The Modulator.

One of the downsides to learning things yourself using the internet or reference books as your guide is that it’s pretty easy to mis-identify something based on poor photographs, incomplete descriptions or information, or just vague or ambiguous wording, particularly if you have a notion about what you’re expecting. In one of the posts I did mid-January, about fungus in the woods in winter, I mentioned a large, creamy, fuzzy mass I observed on the trunk of a tree that I identified as a slime mold. Well, Jennifer over at A Passion for Nature corrected me on this by (correctly) suggesting that it looked like a gypsy moth egg mass.

I went back yesterday to the same area and had another look at it. The particular one I photographed still looked and felt (to my frozen-numb hands) like a cattail thwack with no particular distinguishing characteristics (I didn’t want to try taking it apart because I don’t like to disturb). However, upon closer investigation, I started noticing more of these fuzzy blobs on nearby tree trunks, pretty much all within a few feet of the ground. Some of them had much more obvious visual characteristics that may have led me to the eggs conclusion if I’d seen them first. In the above and the first photo you can actually see the individual eggs wrapped up in all the little hairs that create the fuzzy mass (I think the first photo may actually be hatched eggs from last year? It’s hard to tell, but the dark spots are very pronounced). The hairs are made by the female moth as she’s laying her eggs, and are hypothesized to protect the eggs from potential rodent and avian predators by discouraging them from getting the hairs in their face and nostrils and irritating the skin.

Gypsy Moths aren’t native to North America (like a lot of common wildlife). Rather, they were brought over to Medford, Massachusetts in 1869 by French astronomer Leopold Trouvelot, who also had an interest in insects and was hoping to breed a sturdier, more productive silkworm. Well, like often happens, the moths escaped and it didn’t take them long to settle into the new landscape. They’re now found into eastern Canada as far north as Maine and the Maritimes, as far south as northern North Carolina, and currently west into mid-Wisconsin. When you consider the size of the insect in question, it’s a pretty good area to cover over that period.

The moth’s dispersal is also made more interesting by the fact that the female moth, the recognizable white Gypsy Moth, can’t fly. When she emerges from her pupa she’s full of eggs and way too heavy to get airborne. Male moths (which are brown) can fly, and will travel long distances to reach a female, which they detect using the broad, fluffy antennae that only males possess. These antennae are specially designed to pick up the pheromone molecules released by the female when she emerges. Near a couple of the egg masses I found pupa cases left from the female when she emerged. The cases also have hair tufts that presumably protect them the same way the hairs in the egg mass do.

Still, if the females aren’t moving, then the eggs are going to be laid near where the female emerges, which also doesn’t help much with dispersal. Instead, dispersal is carried out by the caterpillars (weird, eh? The only ones without wings). Caterpillars, during the course of their feeding, climb to the top of the tree and then spin a line of silk which they use to “balloon” on the wind over to the next tree. I can’t imagine this taking them very far, so it would be a very slow dispersal.

This photo (used with permission) is of a female caught in the act of laying an egg mass in late summer. She was found inside a porta-potty, so I can’t imagine the caterpillars would have much to eat when they hatch, but I gather Gypsy Moth females aren’t too particular about where they lay their eggs. The larvae will feed on up to 500 different species of trees, but particularly favour oak. Most of the egg masses I came across were on rough-barked tree species, primarily Black Cherry. Caterpillars hatch from their eggs in early spring, late April into early May. They feed on tree leaves and can be a severe pest in some areas where they completely denude trees of their foliage, particularly since a single egg mass can contain up to 500-1000 eggs. In late June to early July they begin to pupate, and emerge as adult moths after a couple of weeks. Females lay egg masses shortly after emerging, and adults will never eat. Adults die shortly after mating, and the species overwinters in the form of these egg masses.

It’s funny how once you know to look for something, it suddenly seems to jump out at you everywhere. Now that I’m aware of these and what they are, I’ll be keeping my eyes open for them on future walks.

Tag: caterpillars

Life on a maple branch

Cattail thwacks revisited