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Bagworm - Psyche casta

Bagworm - Psyche casta
Newton, Middlesex County, Massachusetts, USA
June 18, 2008
Size: 8 mm
Can these be identified beyond family from their case?

This other one with its head sticking out was within flying range the same month:

Could this one also be this species?

Would somebody summarize this discussion and include it in the info page? I wouldn't be able to do it justice.

Moved from Psychinae. I just finished going through the descriptions and photos of every last North American bagworm (Davis 1964), and I'm convinced. A. confederatra is found throughout the east, but its case is 15-20 mm. The one in the above image looks like a finished case, since it's fastened to the substrate. In both this one and the one in the linked image, the plant fragments are much denser than would be normal for confederatra, and in the linked image they definitely aren't arranged right for that species--they should be clearly diverging. Plus, the whole alien thing is pretty compelling.

Dyar's paper (linked below) says of Psyche confederata, "Case about 11 mm. long, cylindrical, closely covered with rather long, overlapping sticks." Does Davis disagree?

The 11mm size would be a little large but within plausible tolerances for both of mine.

Description from Davis
for Astala confederata (for case of mature larva): "Length 15-20 mm.; diameter 4-5 mm. Silk greyish white, heavily covered, interwoven with minute plant fragments, characteristically overlaid by many longitudinal pieces of grass culms [and] other small stems attached firmly anteriorly, diverging somewhat as they project backward, extending usually most of bag length."

In the illustrated specimen, which I can only assume was carefully chosen as a representative of its species, the base of minute plant fragments is clearly visible, and the longitudinal pieces are sparse relative to all the images I've moved to the Psyche casta page. They are attached only at the front end, and are very clearly diverging.

The Psyche casta case looks just like your two examples (denser, more closely applied longitudinal pieces), and the given size range for cases of mature individuals is 9-13 mm.

So I guess the answer is yes, Davis disagrees. I'm not sure what to make of the difference in opinions, but certainly Davis's is a much more rigorous work.

There are fewer than 30 North American species, so it seems like it should be possible. There are two that I know of that make cases similar to this: Astala confederata and the introduced Psyche casta. I'm not sure how, or if, these can be distinguished, but I think it's probable that yours is one or the other.

There are two references I've been meaning to check out, both of which are at my local library but I haven't gotten around to it yet:

Davis 1964 "Bagworm moths of the western hemisphere." Bulletin of the United States National Museum 244, 233 pages

...Seems like that one should be comprehensive, but often older sources are more descriptive:

Dyar 1893 "On the larval cases of North American Psychidae." Ent. News 4:320-321

Dyar link
Google books page for the volume containing Dyar 1893:

If mine is on Dyar's list, it is clearly confederata, though this one is a little expanded at one and doesn't match his "cylindrical" description as well as the one I linked from here.

I've been tempted to assume they're all the alien, since I see them on the walls of houses all the time, and rarely anywhere else.

As far as I can remember, the only place I've ever seen a reference to confederatra is the Stokes Guide to Observing Insect Lives. I strongly suspect that Stokes used that old paper (I got it from his bibliography) to determine that that's what all those cases stuck to houses are. This paper indicates that casta was first seen in 1931, and in the Boston area, no less. Psyche casta seems extremely likely to me, escpecially given what you found about the apparent range (or at least infrequency of reporting) of confederatra.

A vote for the alien
I'll tentatively go with your alien invader because (1) the Boston area is full of introduced species and I find a lot of them, (2) butterfliesandmoths shows the other one recorded from the Midwest only, (3) the Wikipedia page says Psyche casta likes willow and there is a row of willows next to where I saw the one I linked. But this is all circumstantial. I'll find one of those books. I guess the old books won't show the introduced species so it may take some more investigation after that.


Both are in subfamily Psychinae so I'll move this there for now.

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