Sunday, August 3, 2014

But there will be exceptions....

While I don't intend to post entries in a continuous way, I will make exceptions when I find something of interest, and this is an interesting Lepidostomatid.

I found this larva on Thursday (7/31) in the Rivanna at Crofton: the case was attached to a rock.  What caught my eye was the shape and composition of this particular case: it's round and composed of coarse grains of sand.  It was also quite small -- 6-7 mm.

You'll recall that almost all of the Lepidostomatids we find in the winter and spring have cases that are "four-sided and usually constructed of quadrate pieces of plant material."  (Beaty, "The Trichoptera of North Carolina," p. 81)  That was also true of the Lepido that I found in this location on July the 8th.

True, Lepdostomatids do make cases of sand grains, especially in early instars, like this one that I found at the Rapidan River in December last year.

But most will switch to the more common four-sided case of leaves/bark as they mature.

There is a chance that this is a genus of Lepidostomatid we have not seen before: Theliopsyche.  These larvae are small "up to 6.5 mm", and their cases are "composed of sand grains, curved and slightly tapered."  (Beaty, p. 81)  The genus we're used to seeing is Lepidostoma.  But I'm not really sure.   With Theoliopsyche, the "head [is] flattened with [a] carinate ridge" (Beaty, p. 81), something I don't see on this larva.

Also relevant, on Lepidostoma, the ventral apotome is "as long as, or longer than [the] median ventral ecdysial line;" on Theliopsyche, the apotome is shorter than that line.  (See, Glenn Wiggins, Larvae of the North American Caddisfly Genera, pp. 155 and 159.)  On our larva, the apotome looks longer to me.

I'll continue working on this one.  But at the moment, I think it's just another odd Lepidostoma, a species that's quite different than those we see in our small streams early on in the year.

While I'm at it, it's worth noting that I also found a second Heterocloeon petersi small minnow mayfly -- a species that seems to be fairly uncommon.  This one was a female, and the Heterocloeon "forecoxal gills" were very pronounced in the only decent photo I got.

More striking is the photo of the male nymph that I found in September, 2012.

1 comment:

  1. I think your Lepidotoma in the curved case may be Setodes sp.