| from the July 21, 2008 Newsletter, after a visit to Land
Between The Lakes National Recreation Area in northwestern Tennessee: A MAYFLY SUBIMAGO I saw a mayfly on a rock, apparently having just emerged from its aquatic nymphal exoskeleton, because it was pale instead of the usual dark brown, and didn't seem interested in moving. That's it above. The mayfly's aquatic nymphs are called naiads, while pale, subadult mayflies such as the one in the picture are known as subimagoes, or duns. The subimago stage may last a day or more, then its exoskeleton splits open and the shiny, sexually mature adult, known as the imago, or spinner, emerges. Imagoes of some species, after mating, live just a few hours. In fact, adult mayflies have nonfunctional mouthparts so adults can't even eat; they just mate and die. One reason mayflies rate a special vocabulary with such words as naiad and imago is that sometimes very attention-getting mayfly outbreaks occur, and mayflies provide food to so many birds, fish and other animals that they're very important in their local ecosystems. In fact, the week before when we'd tarried along Ross Barnett Reservoir's western shore in central Mississippi, I'd seen evidence of an earlier mass emergence there, where vast numbers of adult mayflies had ended up clumped in spider webs along shore, shown below. |
| Sometimes beneath lights along shore mayfly bodies pile up a foot or more deep. You
can read about one such outbreak in Wisconsin at http://www.jsonline.com/story/index.aspx?id=457479. On the above page notice that over at the right you can click on the image and see how the mass emergence looked on radar. Many mayfly species exist but I'm supposing that mine belongs to the genus Hexagenia. You can read about mayflies from a trout fisherman's perspective and see some interesting pictures at http://www.troutnut.com/hatch/4/Insect-Ephemeroptera-Mayflies. from the June 19, 2005 Newsletter, issued from the Sierra
Nevada Foothills east of Sacramento, California: I did find a number of flat creatures about the size of a thumbnail, looking like flattened crickets, and sticking to the bottoms of rocks. They bore six legs and the tops of their heads were equipped with conspicuous compound eyes, so it was easy to see that they were insects. They bore no wings or only nubs where wings would someday grow, and three hairlike tails arose from their rear ends. They were the nymphs, or the immature stages, of the Stream Mayfly Family of insects, the HEPTAGENIIDAE. That word "nymph" is a special one used to denote the young of an insect that undergoes incomplete, or simple, metamorphosis, as opposed to complex metamorphosis. In other words, instead of being like a butterfly which goes through the EGG >> LARVA >> PUPA >> ADULT stages, mayflies pass through the stages EGG >> NYMPH >> ADULT. Nymphs usually look like adults, except that they are smaller and bear no wings. There's a lot more about insect metamorphosis under the metamorphosis heading at my Insects Page at www.backyardnature.net/2insect.htm. Google turned up many more pages about stream mayflies than I'd expected, and I wondered why. Then it became clear: Probably 85% of the pages dealt with fly fishing. The quintessential artificial fly tied by fishermen is one modeled after adult mayflies. You can see one such website with pictures of several mayfly species, for modeling purposes, at http://www.flyanglersonline.com/begin/101/part17.html. |