Giant Mayfly

2010 November 13

I found this huge mayfly hanging on the side of one of the campus buildings on June 22, near where I park my bike. This was only about 50 feet from Portage Lake, so that’s probably where it came from.

The body proper is a bit over 3 cm long, and if you include the tail filaments it is almost 7 cm, which for a mayfly is pretty big.

It actually looked a bit different when I first found it – yellower, with less pronounced markings. It pretty much ignored me while I caught it and put it into a jar to take home. It was probably so unresponsive because it was doing this:

That’s the skin that it had shed by the time I got it home and got the camera ready. Mayflies are funny that way. In pretty much all other insects, once they get their fully-developed wings, they are done molting. Flies, beetles, dragonflies, you name it – they don’t get wings until fully mature, and once they have them they are as big as they are ever going to get[1]. Mayflies are different, though: they emerge from their aquatic form as a fully-winged “sub-imago”, fly off to a convenient roosting place, and then molt *again*. Which is what this one was preparing to do when I found it.

It wasn’t much more inclined to try escaping even after molting. I was able to get it up onto my fingertip for photographs, at which point it threw its front legs up into the air and worshipped me like unto a god!

Well, OK, maybe not that, but it did prefer to rest with its forelegs up. I don’t know what it was prepared to do. It looked like it was ready to snatch things out of the air, but mature mayflies don’t eat, as you can see from the head pictures. There isn’t even anything that I would identify as a mouth! Maybe it was preparing to grab another passing mayfly, for mating purposes?

Mayfly wings have their veins in a net pattern, similar to what one sees in lacewings, dragonflies, and ant lions. They also have significantly smaller hindwings than forewings, so the forewings are what provides most of the lift in flight.

In general, it is a lot easier to get IDs on bigger insects than little ones, both because the bigger species are better documented, and because there are fewer large species than small species. This one looks to me like it is in the genus Hexagenia, the Giant Mayflies. They are also called “burrowing mayflies” because their nymphs burrow into bottom sediments to avoid getting eaten by fish. They take one to two years to mature, depending on the climate. The giant mayflies are very popular models for making trout flies, because trout really love to eat them. Particularly when the mayflies are skimming over the surface dropping their eggs.

Further south, these are some of the mayflies that produce massive swarms so thick that they obscure vision and their bodies make the roads slippery, producing a traffic hazard. They are drawn to lights, and so places that are consistently well-lit, like gas stations, can attract millions of them if the conditions are right. I don’t think the conditions are generally right up here, though. We sometimes get mayflies in significant numbers, but I have yet to see anything that I would consider a “swarm”.

[1] A digression about insect growth: People often see a mixture of small and large insects that look kind of similar (for example, small flies and large flies on a window), and wonder whether the little ones are “babies”. The answer is no. If their wings are developed, then they are as big as they are going to get. In those cases, the little ones generally aren’t even the same species as the big ones, they just look superficially similar.

7 Responses
  1. November 13, 2010

    Be careful. These insect worshipping things never work out so well.

  2. November 13, 2010

    I love it. Awesome worshiping pictures. Get another thousand of those little guys and you can start your own religion.

  3. November 13, 2010

    Andy, I think just 12 worshippers would be all he’d need to form an in-sect.

    Would these be the famous mayflies who are alleged to live for just a day? But that would obviously be in their final form, right?

  4. November 14, 2010

    Yes, these are the ones where the adults don’t feed and die within a day or two, but the aquatic nymphs[1] live for an entire year (or, in some cases, two years). A religion for the adults would be an extremely short-lived one. The “in-sect” would never survive without a serious youth outreach effort. And, given that these things are unlikely to end well[2], that is probably for the best.

    [1] I have some pictures of some of the nymphs coming up next week

    [2] It occurs to me that, while the Ten Commandments do have an injunction against worshipping false gods, there doesn’t seem to be anything about allowing yourself to become a false god.

  5. November 20, 2010

    It occurs to me that, while the Ten Commandments do have an injunction against worshipping false gods, there doesn’t seem to be anything about allowing yourself to become a false god.

    Snork! I don’t think the concept of “false” gods was around when the stories that make up Genesis were collected and written down. The executive summary for that era goes along the lines of “I’m your God, not those other gods in the neighborhood. I’ll take care of you if you stay loyal to me.” Monotheism showed up many, many mayfly generations later.

    But I’m certainly going to have fun with your comment the next time I have occasion to write to an old family retainer who’s a Scripture scholar!

  6. Della3 permalink
    January 23, 2011

    Hilarious! Thanks for the laugh!

  7. August 12, 2012

    Great post. I had no idea what I had been taking pictures of or why it had been so still for me the whole time tonight until I found this blog *facepalm* Blogging about it tonight and linking to yours.

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