Exploring the Fatherless Nymphs of *Stenonema femoratum*

Perhaps one of the most often found mayflies on my sampling days are the Flathead Mayflies in the family Heptageniidae. This is one of the largest families with species living around the globe. Around my area though, there are about 100 species or so, and the most common ones I have caught are the species Stenonema femoratum.



A rather roughed up specimen missing a couple legs and part of a cerci.

These nymphs, like most of the Ephemeroptera I've collected, are scrapers that live on the bottoms of rocks and woody debris (which I recently acquired to make my tank more aesthetically pleasing). They are easily identified to family by their shovel-like flattened heads, and flattened bodies. All of these features allow the nymph to resist currents when on top of rocks, and to better cling to rocks when foraging fish flip them over in search of food.

Underside of the nymph.

Despite its humdrum lifestyle, this species exhibits a rather odd type of reproduction from time to time, tychoparthenogenesis. This is an infrequent bout of asexual reproduction in which a normally sexually reproducing female lays unfertilized eggs that hatch into nymphs. This occurs rarely and very few of these eggs actually become nymphs, and yet, this type of reproduction continues on, especially when water temperatures vary.

Hopefully I'll be able to go sampling in a few new locations since I'm seeing the same species over and over again at my two main sites.

Work Cited:

Ball, Shelley L. 2002. Population variation and ecological correlates of tychoparthenogenesis in the mayfly, Stenonema femoratum. Biological Journal of the Linnean Society 75:101-123.