Saturday, May 12, 2007

Chrysalis or Cocoon

Every now and then I come up against evidence suggesting that I'm not as fluent in my native tongue (English) as I thought. Chrysalis? Cocoon? I don't know. So I looked them up in the Oxford Canadian Dictionary:
cocoon: a silky case spun by many insect larvae for protection as pupae
chrysalis: a quiescent pupa of a butterfly or moth; the hard outer case enclosing it

Which didn't help all that much. The silky covering of the one in the yard is tough, but maybe not very hard--so I'll go with cocoon. The case that surrounds the Monarch pupa certainly looks hard--so, chrysalis?

Cocoon, April 28, 2007

During the winter I could see this from the back window, and for a long time thought it was a bird's nest. It's just about 10 cm (4") long. The spirea (flowering shrub, very common in gardens around here) it's in has pretty dense foliage at its peak, so it was not unreasonable to suppose that a bird could've nested there without me noticing. Song sparrows nest all over the place, and I usually can't really pinpoint their locations. Of course, I don't really try--it's rarely a good thing to locate a nest--it either puts it at risk, or it indicates that it isn't well located, i.e., already precarious. Anyway, inspection early in the spring revealed that this was no nest.

It's the cocoon of something big. We had some big stuff around last summer that I know about--and then there are all the things I never saw.... I put this on this morning just in case it can be identified by size and/or location. I check on the cocoon three or four times a day, but still no sign of any change. After a hot week the weather has cooled considerably, so I wonder whether these guys can hold off if conditions aren't great, or if once they get on a certain timetable they can't get off. I'm taking off for a few days next week and I'd hate to miss the emergence.

Here's a link to some photos of an emerging moth of the family that I suspect is represented here, that were pointed out to me in the first response to my id request: Antheraea polyphemus. Mere moments later I got another response, identifying my cocoon as a probable Hyalophora cecropia, based on the relatively open weave. I love (here's a link to my id request and the responses). I have always had extremely quick and helpful responses from that bug community. And cecropia fits--it is certainly well represented around here in the caterpillar season.

Update (later the same day): Because the shape of this cocoon is unlike the other examples of cecropia cocoons at BugGuide, there is uncertainty over the identification. Check the page to see why. And I'll post updates as they develop.

Update #2--next morning: Okay, the issue is resolved. Apparently Hyalophora cecropia shows up in two different kinds of cocoons--neat, narrow ones, and big baggy ones (such as mine). So Robin moth it is--very nice. I've got my fingers crossed that I actually get to see one of these beauties. For more about the moth, check out its species page at BugGuide.

And just one more: Here's a link provided by Bev of Burning Silo in the comments below, to another good site for cecropia info.

Here's a post I wrote last August about the cecropia caterpillar pictured below. Apparently the adult moths only live a couple of weeks, so all the more I hope I get to see this one emerge!

hyalphora cecropia
Hyalophora Cecropia, August 2006


burning silo said...

I too would say it was a Hyalophora cecropia cocoon. I've seen cocoons that are both fairly rigid, as well as the more bag like ones. David Wagner mentions that sometimes these caterpillars also make a bag-like cocoon in the grass around the base of apple trees in autumn. I've never seen one like that myself, but must remember to watch for them. I found one cocoon attached to meadowsweet in the field here, but also another attached to some Buckthorn branches when I was cutting it out from beneath some Jack pines. I almost tossed the stick into the brush heap before noticing the cocoon attached. I've brought it in to the screened porch on our house where it will probably be safer until the moth emerges. My usual way of deciding whether it's chrysalis or cocoon is that if the structure has to be "made" (spun) by the creature, then I usually call it a cocoon. If the creature actually turns into the structure (as in the case of a Monarch butterfly) where the creature just undergoes change and morphs into its pupal struture, then I call it a chrysalis or pupa. I don't know how technically correct that explanation is, but that's how I figure it. (-:

Pamela Martin said...

Thanks, Bev. I like that--makes more sense put in terms of what the larva actually does.

Reading around I found that in southerly regions cecropia have 2 flights a season (as I understand it, 2 generations), northerly, one. Do you think we're a one generation region? And if so, is it unlikely this one will emerge before June or July?

burning silo said...

I'm sure there would just be one flight a year in this region. The best info on the behaviour of all of the large moths is on Bill Oehlke's site (he's in Nova Scotia). Here's a link to his page about Cecropia moths. There's tons of good info on flight dates, reproduction, etc...
This page is also pretty good.
I'm actually contemplating keeping the one cocoon until the moth emerges and trying to capture a male and keep it in the porch with the female (males are supposed to fly for miles to a female). I would then try to collect eggs and rear the caterpillars. I wouldn't normally bother, but I've recently read some statistics on how few Cecropia caterpillars make it to the cocoon, and then emerge as moths, that it might be nice to see if I could successfully rear a better percentage.

burning silo said...

I'm not sure if the link to Bill Oehlke's sight worked, so here it is again. Hope that works.

Pamela Martin said...

Bev, thanks for the link--that is a nice clear page of info. And the cocoon pictured there is much like mine.

What an adventure it would be to breed these guys, I hope you decide to try it, and of course, document it.