Sunday, December 21, 2014
It may have been a VERY odd Lepidostomatid: genus Theliopsyche
Interesting. Almost every -- well, "every" as far as I know -- Lepidostomatid (common name: Bizarre caddisfly) I see is genus Lepidostoma. The genus is defined by the case that it makes: "four-sided and usually constructed of quadrate pieces of plant material. Early instars may have sand case." (Beaty, "The Trichoptera of North Carolina," p. 81) However, there is a critical anatomical feature as well: "Head with ventral apotome as long as, or longer than, median ventral ecdysial line." (Wiggins, Larvae of the North American Caddisfly Genera, p. 155) That feature is easy to see on the head of this larva preserved in my collection.
Yesterday, I decided I had best check the head on that odd larva from Friday, and here's what I saw.
That ventral apotome is quite clearly shorter than the median ventral ecdysial line! That suggests that this little larva (~ 6 mm) was genus Theliopsyche, not genus Lepidostoma.
Beaty on Theliopsyche: "ventral apotome of head shorter than median ventral ecdysial line." (p. 81)
Wiggins: "Study of our larval material leads to the prediction that Theliopsyche can best be distinguished by the length of the ventral apotome of the head which is shorter than the median ventral ecdysial line. Length of larva up to 6.5 mm." (p. 158)
Beaty notes that four species of Theliopsyche are attested in North Carolina -- corona, epilomis, grisea, and melas. But only one larva has been described to date -- T. melas -- and melas has a "head [that is] flattened with [a] carinate ridge." (p. 81) Do we see a carinate ridge on our larva?
Possibly, but it's questionable, and that head doesn't look very flat. So T. melas appears to be out, but we can't rule out some other species. (According to natureserve.org, T. grisea has been found in Virginia as well as T. melas.)
We can't say for sure that our larva was a Theliopsyche. But the ventral apotome/ecdysial line ratio certainly corresponds to Wiggins' key to the genus ID. And, this larva was certainly different than the Lepidostomatids we typically see in this stream: their heads are always burnt orange,
The head on this larva was clearly dark brown.
Stay tuned. Oh, two other things. 1) Theliopsyche larvae make cases "composed of sand grains, curved and slightly tapered" (Beaty, p. 81), but as I noted at the end of the previous entry, this larva had temporarily moved into a 3-sided leaf case vacated by P. gentilis. And 2), on habitat -- "Larvae and pupae of T. melas were collected in the clean gravel bed of a small spring run. Localities for other species of Theliopsyche indicate that they probably live in similar habitats." (Wiggins, p. 158) We were clearly in the right place to find them.