August 11th, 2006
go away and leave me alone!
This morning, when I wrote the first piece about Black Swallowtail caterpillars, I forgot to mention something rather interesting about their behaviour and appearance. Fortunately, I was reminded this afternoon when my mother, who has been visiting and became involved in the daily caterpillar chores, noticed that the Swallowtail caterpillar “grew horns” when disturbed.
I never knew about Black Swallowtail’s osmeterium — a tentacle-like head gland — until last fall when I happened to disturb a caterpillar concealed in some grass in the perennial garden. It extended an odd looking set of golden antlers and thrashed around a bit — no doubt, trying to give me the “Go away and leave me alone” message. I was unable to photograph it that day, but this little caterpillar seemed quite eager to display this gland, although it looked more like stubby cow horns. It’s not a full-sized caterpillar, so I assume the osmeterium will become much larger by the time it pupates. The gland is supposed to exude an unpleasant odor that wards off some predators. I didn’t notice any particular odor, but one can only hope that it would be enough to put off an Assassin or Stink Bug.
Edit: Wayne from Niches posted a comment about other species of swallowtail caterpillars which he has photographed at Sparkleberry Springs. There are some wonderful photos of the caterpillars with and without their “headgear” on display. These are of Pipevine Swallowtails (Battus philenor), and these are of Giant Swallowtail (Papilio cresphontes). Definitely take time to have a look at Wayne’s pages and photos. By the way, I should probably note that in our posts, Wayne and I have used different spelling of the term used to describe the fleshy gland which can be extended from the head area of a caterpillar. Both osmeterium and osmetrium seem to be in common use.
Tags: Black Swallowtail caterpillar, Papilio polyxenes, osmeterium, osmetrium
August 11th, 2006 at 11:26 pm
Wife and I are thoroughly enjoying your insect blogs Bev, great stuff, or have I said that before!
August 12th, 2006 at 12:34 am
That is totally far out.
August 12th, 2006 at 6:16 am
I take great joy in tapping the little guys on the head with a grass stem to make them stick those things out. Different swallowtails have differently colored ones, too.
I wonder what the osmetrium becomes during metamorphosis?
August 12th, 2006 at 11:02 am
Duncan – Thanks! I’m having fun with the monarch experiments but thought others might be starting to find them a little boring! (-:
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Dave – Yes, actually it is pretty far out. As Wayne has commented, it’s kind of amusing to see these things pop out as they seem to come out of nowhere.
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Wayne – Ah, I see that I’m not the only one who finds them amusing. I would love to see some of the other species of swallowtails as the photos of a few of them look pretty cool.
Last night, I touched this caterpillar with the stalk of a Queen Anne’s Lace and it reacting with such ferocity. The “horns” really came out this time — and they are of a normal length, btw… and it sort of slashed quite fiercely at the stalk. I was thinking, “My, you’re quite the grumpy little devil!”
Very good question about what they become during metamorphosis. Most parts seem to have some future expression, but I’m not sure about these. Must do some checking into that.
August 13th, 2006 at 10:56 am
Bev – there’s a photograph here of the Pipevine Swallowtail’s osmetrium.
And here of the Giant Swallowtail osmetrium – look good enough to eat!
August 13th, 2006 at 11:57 am
Wayne – thanks for posting links to both of your pages on swallowtail caterpillars. I’ve just edited the above post to include links to both pages as it would be nice for everyone to see other examples of similar caterpillars.
February 15th, 2007 at 10:23 pm
“Stubby cow horns” and “‘My, you’re quite the grumpy little devil!’”- Hilarious. It must be so exciting and exhilarating to see the little critters poking those fierce little horns out! =)
February 15th, 2007 at 11:59 pm
Laiku – Yes, it was quite exciting to see the horns sticking out. It happens quite suddenly, and then it retracts them just as quickly. I’m hoping to raise a few more of this species this summer, but will try to find early season ones that will pupate and emerge as butterflies over the summer — instead of trying to keep the late season ones over the winter again.
February 17th, 2007 at 5:50 pm
I saw those golden antlers too, once. I didn’t smell or feel anything though. Is it just to scare predators away? Becuase it didn’t deter me.
February 17th, 2007 at 11:13 pm
Laiku – One thing I noticed… not right when I wrote this, but a few days after, was that there was an odd smell that was a little bit like tangerines when the horns were extended. I think there is probably some chemical that may be released when the horns are exposed. I think I found something about this on the internet and that the chemical is similar to something in oranges — perhaps something a bit stinging, like the vapour that is released from an orange peel if you squeeze it. No doubt, some kinds of predators would not like the smell or taste. I think the menacing look of the horns may also scare smaller predators.
February 19th, 2007 at 3:42 pm
Oh…that’s very smart! But it doesn’t seem to really affect us people.
February 19th, 2007 at 4:04 pm
Laiku – No, but I wonder what it might be like if we were very close to the caterpillar when the scent is released. It might not be too pleasant — although I would think the amount released is probably quite small. If you’re interested in such things, there’s quite a good book by Thomas Eisner (et al) called Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures. It’s probably available through your library system. Most of the book is about how various insects protect themselves from predators — usually through the release of chemicals – sprays, scents, fluids that burn, etc… It’s very interesting!!