A female subimago of March Brown (<i><a href="//commons.wikimedia.org/wiki/Rhithrogena_germanica" title="Rhithrogena germanica">Rhithrogena germanica</a></i>) of family Heptageniidae. Mayflies are insects which belong to the Order Ephemeroptera (from the Greek ephemeros = "short-lived", pteron = "wing", referring to the short life span of adults). They have been placed into an ancient group of insects termed the Paleoptera, which also contains the dragonflies and damselflies. They are aquatic insects whose immature stage (called naiad or, colloquially, nymph) usually lasts one year in fresh water. As shown a Mayfly on a Rough Horsetail (<i><a href="//commons.wikimedia.org/wiki/Equisetum_hyemale" title="Equisetum hyemale">Equisetum hyemale</a></i>) which is a perennial with a rhizomatous stem formation native to the northern hemisphere. Identification:  Dr. Arne Haybach at www.ephemeroptera.de (thanks!)
<a href="//commons.wikimedia.org/wiki/User:Richard_Bartz" title="User:Richard Bartz">Richard Bartz</a>, Munich aka <a href="//commons.wikimedia.org/wiki/User:Makro_Freak" title="User:Makro Freak">Makro Freak</a> <a href="//commons.wikimedia.org/wiki/File:Makro_Freak_bar.jpg" class="image"><img alt="Makro Freak bar.jpg" src="https://upload.wikimedia.org/wikipedia/commons/8/8b/Makro_Freak_bar.jpg" decoding="async" width="80" height="15" data-file-width="80" data-file-height="15"></a>, cropped by <a href="//commons.wikimedia.org/wiki/User:Fir0002" title="User:Fir0002">Fir0002</a>
CC BY-SA 2.5
<span class="int-own-work" lang="en">Own work</span>