The gradual exodus from the ponds that began with the midges a few weeks ago continues with the first adult mayflies.
I’ve always called these creatures fishlies; apparently this terminology is unique to the Great Lakes area of the U. S. and Canada. They belong to the order Ephemeroptera, and they are truly ephemeral: after they emerge from the water they live only a few days, often less—just long enough to mate, lay eggs, and die.
It has been windy these past few days, and the mayflies cling to my enclosures, their wings held tightly together. Sometimes one is blown off and falls to the water’s surface, but they are so delicate that they cannot break the surface tension. They simply allow the wind to push them to the other side of the pond.
Many insects begin their lives underwater as larvae called naiads or nymphs and undergo a drastic change when they finally become adults. Over the course of my field season many species will leave their watery nursery. They will also leave behind their exuviae, the moulted nymphal skins that they shed as they emerge. Like the mayflies, many will have spent most of their lives, possibly several years, underwater but will only spend a short time flying before they reproduce and die.
Insects are not the only pond dwellers who metamorphose. The frogs, of course, will too, but not for a while. The first clutches of eggs have just hatched; the tadpoles are barely a centimetre long. Right now, they are smaller than many of the insect nymphs, who will in fact prey on them.
Here’s one of the smaller kinds of nymphs. I think it’s a stonefly. Mayfly and damselfly nymphs look very similar. Dragonfly nymphs tend to be much larger—two or three centimetres long—and squatter, with an oddly crustacean appearance.