Ruby Tiger Moth

2010 March 27

Back at the end of February, S_ and Sam went out ice-fishing. When they were done and packing everything into the car to come home, Sam spotted a caterpillar crawling across the snow. So, she caught it and brought it home for me to see. It was a black-skinned, furry caterpillar, but the fur was in pretty rough shape, with most of the hairs knocked loose, and so it didn’t really have any distinguishing features. Some of the hairs were black, and some of them were more reddish-to-blond, but that’s about all that could be made out. It was clearly one of the “wooly bear” type caterpillars, but only about half the size of the most well-known type (the Banded Wooly Bear). It was most likely going to grow up to be one of the many species of Tiger Moths, but which one? So, we decided to raise it to adulthood to find out.

We put it in a jar along with some reasonably green grass that we dug out from under the snow, but it didn’t eat any of the grass. Instead, within two days it spun itself a cocoon and pupated. The cocoon was made out of a mixture of new silk and the caterpillar’s hairs, and was about twice as long and wide as the pupa that was faintly visible inside.

Then it was just a matter of waiting. Finally, on March 22, it came out of the pupa, and this is what we saw:

The upper side was a dark, slightly reddish brown, but there were some hints that the underside was more colorful. It got to running around on the table and fluttering its wings, showing that under the wings it was a deep red color. The best picture we could get was by holding it in forceps and turning it over, like so:

This also made it possible to see that the forewings were only lightly scaled, and almost translucent. And, looking at the face, the antennae were white. This was not an artifact of the camera flash reflecting off of the antennae, they really were that white.

Given all those details, it looks like a Ruby Tiger Moth, Phragmatobia fuliginosa. This is one of the northern tiger moths, and while the record of where they have been documented is spotty, they have been found not too far from here in the past. The things the caterpillars like to eat are mostly considered weeds (goldenrod, dock, plantain, etc.), so their life history evidently hasn’t been very well examined. It sounds like the adults are another one of those moth species that don’t feed, depending on their fat reserves from the larval stage to carry them through long enough to breed.

Anyway, we let it go after we were done with the pictures. It’s probably going to be too early to find a mate, what with having been kept in the warm indoors while all the other members of the species are still out in the cold, but maybe it will live long enough to get lucky.

11 Responses
  1. Alan permalink
    March 27, 2010

    One of my favourites!
    I managed to photograph their complete life cycle a few years ago as can be seen here:

  2. March 27, 2010

    Should have mentioned, that was in Scotland by the way. I did not realise they were also found in north America. Are they introduced there or is that part of their natural range?

  3. March 27, 2010

    The references I’ve found just say that they have a Holarctic distribution, meaning that they are found both in North America (Nearctic) and Eurasia (Palearctic). I’m not seeing any suggestion that they were introduced by human activity, so it must be part of their natural range. I suspect that they are one of the species that were cold-hardy enough to cross the Bering Land Bridge in the last glacial period, although I don’t have any idea whether they crossed it going west, or going east.

  4. March 27, 2010

    Alan: Your complete life history of these moths is excellent! Given the rough condition of the caterpillar we started with, I really didn’t know what they normally looked like. Thanks very much for the link!

  5. March 28, 2010

    I wonder what the chemical composition of the outside of the antenna is that gives it a white sheen.

  6. kaiakai permalink
    March 18, 2012

    My brother and his son found a caterpillar on the snow a few weeks ago here in Estonia. After much deliberation about what to do with the caterpillar, they decided to leave it with me… In any case, you’ve described our experience exactly. Our ruby tiger emerged from its cocoon today (March 18). It’s only +2C out, so I’m hesitant to let it go outside.

  7. Laura permalink
    September 26, 2015

    How long do these usually stay in a cocoon for?

  8. September 27, 2015

    Ours came out after about 3 weeks. I expect that it varies with temperature, though.

  9. samson permalink
    December 11, 2016

    how long do they stay in there cocoon. also i found them outside and they were nearly frozen because this was in winter this year (now) so i took them inside and put them in my faunarium with leaves water and salad one has pupated and is still in the process the other two are just doing nothing what shall i do??is it a matter of waiting?

  10. December 12, 2016

    Ours came out of the cocoon after about 3 weeks, so that’s probably how long it will take for the one that pupated. As for the other two, they are probably still primed to hibernate for the winter, and may need to go through a cold spell before they will pupate. You could put them in the refrigerator for a couple of months and then bring them out again.

  11. Taylor Whisenhunt permalink
    April 18, 2018

    Our just came out of cocoon today. We found is March 23rd outside here in Alaska and it went into cocoon on March 25th. The one I have it very red and beautiful with the slots underneath it’s wings. My kiddos named it big red and tho it’s outside it has yet to fly away yet. Wish I could comment a picture as it really is gorgeous.

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