Last August, I was on the way to a wetland plant plot with fellow field botanist Sally Shaw, when Sally spotted some suspicious white patches on a frond of New York fern (Thelypteris noveboracensis or Parathelypteris noveboracensis, depending on who you ask).
Flipping the frond over, I saw that these white patches were each connected with a silken gallery spun along the length of a midrib (pinna rachis).
This webbing was produced by moth larvae that were feeding on the fern’s spores, and the white patches on the upper surface were apparently used for disposing of frass and empty indusia (spore coverings—the yellowish things in the photos below).
I knew this sounded familiar, and when I got home I found the page on microleps.org that discusses these moths. Stathmopoda is a genus that has been shuffled from family to family over the years, and is currently placed in Stathmopodidae, a family with 100 species worldwide* but just three in North America as far as I know. Of these three, Stathmopoda aenea and S. elyella feed on fern spores as illustrated above, and the introduced European species S. pedella feeds on alder seeds. New York fern is not a documented host for any of these (see Terry Harrison’s discussion of host plants at the above link).
I managed to catch a larva out of its silken tunnel long enough to get a decent photo of it…
…and here is one disappearing into the denser part of its webbing, which leads to the escape chamber / refuse pile on the upper surface of the frond.
Six days after I collected the frond (on August 18), the larvae turned orange, signalling that they were done feeding and ready to spin cocoons.
I gave them a nice jar of soil with a crumpled-up piece of tissue paper so they could choose whatever pupation site they liked, but this one opted to spin its cocoon just under the lid of the jar.
In early May, the first adult emerged.
This moth’s posture seems a little odd, but all stathmopodids have the habit of resting with their hind legs raised. In fact, the name Stathmopoda comes from Greek words meaning “balance” and “foot.” Pending examination of the specimen by an actual lepidopterist, I’m going to assume this is S. aenea—yet another of the many species described by Annette Braun that I’ve had the pleasure of meeting.
* Heikkilä, Maria, Marko Mutanen, Mari Kekkonen, and Lauri Kaila. 2014. Morphology reinforces proposed molecular phylogenetic affinities: a revised classification for Gelechioidea (Lepidoptera). Cladistics 30: 563–589.