Sunday, April 9, 2017

Back from Montana with some beautiful insects


I was fishing in Montana last week -- and looking for insects -- and I found some beautiful nymphs, including two large winter stoneflies (Taeniopterygidae) that I've not seen on previous trips.

Number one is this beautiful nymph that I found last Wednesday on the Bitterroot River.  Personally, I think the colors are stunning, and as you can see by the black tips on the wing pads it was fully mature.


From what I can tell, there are five species of "Willowflies" (Taeniopterygidae) in Montana (http://fieldguide.mt.gov/displaySpecies.aspx?family=Taeniopterygidae): Taenionema pallidum (Common Willowfly), Taenionema pacificum (Pacific Willowfly), Oemopteryx fosketti (Saskatoon Willowfly), Taenionema uinta (Uinta Willowfly), and Doddsia occidentalis (Western Willowfly).

As will become clear in a moment, this is not a Taenionema nymph.  Taenionema nymphs, for one thing, are dark brown in color as we have seen with the species we find in our own streams, Taenionema atlanticum.  This one.


That means our nymph is either Oemopteryx fosketti or Doddsia occidentalis.  Both Doddsia and Oemopteryx are described in detail in Stewart and Stark (Nymphs of North American Stonefly Genera, pp. 227-235).   The nature of the laciniae and the mandibles is important in deciding on identification -- unfortunately, my microscope won't allow me to see them very well.  However, there are two other things to consider.  1) The mesosternums aren't the same.  On Doddsia, the stem of the mesosternal ridge is "about equal in length to each arm"  while on Oemopterx, the stem is considerably shorter.  This looks like a Doddsia nymph.


And 2) the shape of the ventral plate is on Doddsia is "semi-ovate", not so on Oemopteryx (see the illustrations on pp. 231 and 234).  We have an oval plate on this nymph (note how the top edges curl in).


While I can't be sure of my identifcation, if I had to guess, I'd say this is Doddsia occidentalis, the Western Willowfly.

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This is nymph number two.


While I found nymph number one in the big, wide Bitterroot River --


nymph number two -- and I must have picked up 50 of them in a matter of minutes -- was in a small stream by our hotel, Grant Creek.


I'd bet the house that these were Taenionema large winter stoneflies.


The color alone is a pretty good sign.  The "brown body color" -- noted in every key that I've seen -- is noted by Stewart and Stark (p. 241) as one of the key "Diagnostic Characters".    Again, I can't see the laciniae and mandibles as I would like, but I can note three other things that help with this genus ID.  1) Beaty notes ("The Plecoptera of North Carolina," p. 23) that the "posterior margin of [the] pronotum [is] wider than [the] anterior margin."  Pretty clear that it is.


2) the sternal plate of the male is "broadly triangular in posterior half and bearing short erect hairs in posterior two-thirds." (Stewart and Stark, p. 241) That's a match.


And 3) there's the legs.  "Legs with continuous, silky dorsal fringe, sometimes sparse on tarsus." (Stewart and Stark, p. 241).  That's also a match.


Taenionema for sure.  Which one -- pacificum, uinta, pallidum? -- I haven't a clue.  I can't find any keys that take this to the level of species.  We need Steven Beaty to move to the West.  (:

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The fishing was great.

The Skwala stoneflies were hatching.  Photos of Skwala nymphs and an adult in my next entry.

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