Mystery Solved. Sort of.

Last summer I wrote about an intriguing find I discovered on a blade of grass. I wasn’t able to identify the hard, odd-looking, black-as-coal structure but wondered if it might be an egg case of some kind. A short time after that I discovered a second one in the same area — a roadside ditch next to a cow pasture.

Thanks to Alberta entomologist and author John Acorn I now have an answer. It’s probably the egg case of a horsefly or deer fly. (You know, those pesky summer spoilers that can take a chunk of meat out of your arm or leg or wherever they decide to dine.)

A check with Bug Guide confirmed the ID. Apparently these flies deposit their egg masses on vegetation that overhangs water or wet ground (the latter in the case of the ones I found). When the eggs hatch the larvae drop to the ground. (Or into the water, I guess.)

WikiPedia added more to the story …

Both males and females engage in nectar feeding, but in addition to this, females of most species are anautogenous, meaning they require a blood meal before they are able to reproduce effectively. To obtain the blood, the females bite animals, including humans, while the males are harmless. It takes the female about six days to fully digest its blood meal and after that it needs to find another host. It seems that the flies are attracted to a potential victim by its movement, warmth, and surface texture, and by the carbon dioxide it breathes out. The flies mainly choose large mammals such as cattle, horses, camels, and deer, but few are species specific.

And that’s where the story ends for now. I still have questions. For example, how to the eggs get out of that hard case? Does it dissolve after a time? Do they eat their way out? Can they survive in both water and land?

More will be revealed, I’m sure.

Egg Case

The Tortrix moth infestation that occurred this spring was of almost biblical proportions. Many of the aspen forests were completely denuded by the ravenous caterpillars (aka larvae).

They pupated next, then after a short respite, the adult moths appeared. Thousands of them. And of course, their main goal was mating and egg laying, which they did in grand fashion.

In fact, so intense was the drive to lay eggs, they did so in the most unusual places. We discovered egg cases, like the one above, on the windows of the house, on the siding and on the vehicles.

Many of these eggs never hatched. The ones on the south-facing windows, for example, simply got too hot. But not before some activity occurred.

The egg cases were all about the same size as this one — 1.3 cm or so long (0.5 in). The original egg case was a lime green — some of that is still visible. I’m assuming it was plant material to feed the newly hatched larvae.

The comma-shaped figures are the newly hatched black-headed larvae. Some of the cells are empty — perhaps they survived?

Mother Nature’s Natural History Show is a wonder. Glad I caught this episode.


Large aspen tortrix   Choristoneura conflictana

What is This?

Okay. I’m stumped: What is this? I bet someone knows.

Found it this morning on the back of a large, dry grass blade. The grass was upright — I bent it over to take the photo.

I’m guessing an insect egg case. But what insect?

It’s hard. Coal black. About 8 mm long (about 0.3 inch), slightly narrower side to side. Rippled surface. A slight “pinch” at one end.

IMG_6395 - Version 2

Guesses?