Closeup insects from the Namekagon River
Ephemerella subvaria (Hendrickson) Mayfly Nymph
View 3 PicturesThis is one of the nymphs I collected doing something very, very strange on March 17th 2004. In the middle of the day, around 2 pm, in the water right around my feet I watched lots of Ephemerella nymphs clumsily swimming up all the way to the surface and then just kind of drifting and wiggling around in the water column. None hatched. They seemed to do it more intensely when the sun was out. It wasn't the time of day for the normal invertebrate drift phenomenon, and as far as I know invertebrate drift doesn't involve this kind of clear effort to swim all the way to the surface. I didn't need a net to catch them, I just reached down into the water and grabbed them with my fingers just below the surface.
The prominent abdominal tubercles (
A few (not all) of the abdominal tubercles on this
Ephemerella needhami nymph are circled. They are especially large in this species.
Tubercle: Various peculiar little bumps or projections on an insect. Their character is important for the identification of many kinds of insects, such as the nymphs of Ephemerellidae mayflies.) aren't quite black, though, and the general color is a dark brown, though I saw nymphs with all Hendrickson color stages behaving strangely. Epeorus vitreus (Sulphur) Mayfly Nymph
View 3 PicturesI suspect this is an Epeorus vitreus nymph. At the current instar (Instar: Many invertebrates molt through dozens of progressively larger and better-developed stages as they grow. Each of these stages is known as an instar. Hard-bodied nymphs typically molt through more instars than soft-bodied larvae.), it's tough to make out the pair of dots on the tergites (Tergite: The top (dorsal) part of a single segment on an insect's abdomen when it consists of a single chitinous plate (sclerite), or an individual sclerite if the segment has more than one.) which signify that species, but with zooming and contrast enhancement they become evident.
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