The Mayfly Challenge on April Fool’s Day

It’s April Fools Day and the weather tried to trick us into thinking it is still winter by adding at least two inches of snow to our world that is for the most part . . . still covered by at least a foot of snow. In some places it is even deeper. In others, bare ground and leaf litter are visible. And evergreen plants like Goldthread and Wintergreen and Partridgeberry show off their shades of green.

But this isn’t about snow or flowers. Instead, I want to take you into the water. YES. It’s time to stop tracking on a regular basis and begin squatting beside open water and peering in, which a friend and I did just this week when we were checking on beaver activity.

We didn’t spy any beavers, though there was lots of activity including these logs underwater, which told us the family was still in residence. But . . . take a look at the logs. Yes, you can see the chew marks left by the beavers as they dined on the cambium layer. There’s so much more though.

Each of those dark spots on the logs . . . Mayfly larva! A fly fisherperson’s delight. Ours as well. We know from experience because this past year we’ve dipped D-nets into streams in all seasons, that the larval forms of aquatic insects are alive and well whether there is a foot of ice or no ice. But where the ice has started to melt (and that’s not everywhere yet, though this week is supposed to warm up), life that has been there all along is emerging before our eyes.

Did you know that there are 614 species of Mayflies in New England? Eggs are laid in the water, where the larval form or nymph develops. #1.Shows the egg that had been deposited on the bottom maturing into a nymph. #2 is the nymph growing  in stages called instars until it matures. By #3, the mature nymph or emerger swims to the surface. Some species shed their skin and becomes a dun or subimago on the water’s surface. First It floats until its wings are dry enough for flight. This is a unique stage in the insect world as only Mayflies are fully winged before the adult stage. Others climb upon vegetation or an upright object to everge. For #4, you can see that the dun flies into bushes or trees along the water’s edge, where it sheds its skin and, #5, becomes an adult known as a spinner or imago. #6. The spinner flies off to join the mating swarm. #7. After mating, the female spinner dips her eggs on the water’s surface, and they fall to the bottom where it takes anywhere from ten days to months to hatch. Finally, #8 depicts the end for both male and female spinners fall to the water’s surface and die after mating. Keep in mind, this is a general description of a Mayfly’s life cycle. 

If you look with a keen eye you can see some of what I found one day–at least ten Mayfly nymphs on a leaf. I’ve used black arrows to point to some of them. 

Here’s your challenge. Quiz #1: I’ve done the squatting for you. See if you can locate at least one Mayfly nymph in this photo.

Not all nymphs are equal–in size that is. Remember, there are 614 species. Again, if you look closely, you’ll see that this one large nymph is surrounded by two smaller ones. Notice the tails. Mayflies have elongated bodies with 2 – 3 very long, tail-like appendages called cerci at the end of their abdomens.

Here’s another reference for size as the large beetle is a Predacious Diving Beetle and there are three small Mayfly nymphs in the picture.

This is a dun or subimago who had just flown from the water. Well, I should correct that as I had picked it up from the water’s surface and let it dry its wings while resting on my finger. And then I helped it to a nearby shrub. Look at those wings.So many people don’t like Mayflies, but I find their structures and life cycle to be amazing. Take note of how “cloudy” the wings are. That’s how I know this is a dun. 

Mayflies, of course, don’t just land on bushes and trees, but some species may choose stems or rocks upon which to transform. Others meet obstacles along the way, including my pants. But again, notice those wings–another dun or subimago. And notice how the hind wing is so much shorter and rounder than the forewing.

A little bit about Mayfly anatomy. Like all insects they have a head, thorax, and abdomen, whether as a nymph, subimago, or adult (imago). The head typically is for seeing and feeding, though while Mayflies feed in their nymphal form, any mouthparts in the adults are reduced or non-functional. The thorax is the section of the body that supports three pairs of legs and two sets of wings–a forewing and a hindwing and therefore it’s located in the center of the body. In the larval or nymph form, the abdomen features gills, which are absent in the older two molts. And you can see the tails attached to the end of the abdomen. Notice, too, the gender ID. So the abdomen bears the reproductive structure and in some insects it also carries the digestive tract. 

So, Quiz #2: Male or female?

Sometimes the safe place isn’t a shrub or some other natural setting for a final molt, but rather the screened porch at our camp. Often, early in the morning, as I sit in a rocking chair to sip coffee, I’ll notice a visitor on the outside of the screen. And not just in May. These were in August.

Mayflies often molt at night by breaking out through the top of the thorax. In the process, the Mayfly pulls a fresh set of wings from inside the subimago wing cuticle. How cool is that? 

Here’s a look at the discarded exuvia or shed skin and you can see the adult to the left.

Here is a clearer view of the adult or imago, which, you remember, will only live long enough to join the mating swarm, mate, and then die.

Notice how clear the wings have become.

And those conspicuous eyes. They are like a mini-set of dumbbells. But no mouth because with such a short life-cycle, there is no need to feed.

This is a shed skin I found on the surface of a swampy section of a river.

And right next to it, the dun or subimago crawling away as its wings dried.

Quiz #3: What stage is this? And is it male or female?

Quiz #4: And what stage is this?

Not all Mayflies die on the water as there are other hazards one might encounter such as this very sticky spider web.

That’s all I have to say about Mayflies for today, but going forth, expect more of these tiny critters to appear in this space. Along with others like dragonflies and cicadas and robberflies and . . . I can’t wait. Oh yeah, and it’s almost vernal pool season too.

Thanks for taking the Mayfly Challenge on this April Fools Day.