Friday, April 20, 2012

Not Quite Ready to Fly: Maturing Insects in a Small Stream in Sugar Hollow

As we saw yesterday, the prolific spring hatches have already begun.  But today I just saw the insects that are still getting ready to go.  Above -- a beautiful, big, Common stonefly (family: Perlidae): Acroneuria abnormis.  Notice how the wing pads have started to darken and how pronounced the abdominal banding has become (on A. abnormis nymphs, the abdominal bands are dark at the front and light at the back.)  This nymph was about 1 1/4" long, and it will hatch as a "Golden Stone" in June or July.

And while I was expecting to see more adult green stoneflies (Chloroperlids), since they were all over the rocks yesterday, today I only ran into maturing nymphs.  But it's an insect that is really quite handsome.

In the photos I took yesterday of the adults, the three black dots on the head -- the ocelli -- were very prominent -- the head is lacking in any other design.

When we take a close look at the head of the nymph we see that this a feature that just carries over with the emergence.

Probably not a bad time to remember what these, now beautiful, stoneflies looked like back in November:

Why, they're just like us: the older they get the better looking they are (!)

Two more insects that are clearly maturing and getting ready to hatch: the freeliving caddisfly larva Rhyacophila fuscula, and the Northern case-maker, genus Pycnopsyche.  The former was also about 1 1/4" long and will surely enter pupation any day now: the latter has fashioned a case of pebbles, firmly cemeted together with silk, which it will soon seal off for pupation.

And then, we have the spiny crawlers.   At the moment, there are so many of them in the leaf packs and on the rocks that it's hard to find anything else.  I've got to think that the spiny crawler hatch, which normally happens in May, is the most prolific hatch that we see in central Virginia!  The nymphs I was seeing today were, as they were yesterday, the species E. dorothea.   They seem to have replaced the E. invaria nymphs that we saw earlier in the season, a fact that Steven Beaty seems to confirm: "Ephemerella invaria appears to emerge earlier than E. dorothea, with peak abundance in March." ("The Ephemeroptera of North Carolina," p. 27).   Anyway, a token picture.

The only "youngster" I found -- other than a number of "teenage" Giant stoneflies -- was the Perlodid stonefly, Isoperla holochlora.

 I. holochlora is, I think, the last Perlodid stonefly of the season to show up in our streams, and according to Beaty ("The Plecoptera of North Carolina,"), we can see these in our streams right into August.  The mature nymph in the photo below was found on June 13th, 2011 in the same stream I went to today.

(Below: a mature common stonefly and an immature Isoperla holochlora Perlodid stonefly.  Quite a difference in size!)

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