Mayflies are an Order of insects (Ephemeroptera) so named for their short lives as adults, which may be only a day or two after years in the water as nymphs (also called naiads). They may emerge simultaneously in enormous numbers. They are the only insects besides True Flies (Diptera) which may have only two wings, in some species, instead of four . A unique aspect is that they are the only insects that may shed their skins when fully winged. The preadult stage is called the subimago, while the sexually mature, fully adult is called the imago. Here is a table with photos of species, arranged in families. Images are available for prints, publications, websites and videos are available for TV and film.