Saturday, August 30, 2008

Luna Moth Caterpillar

The luna moth is a remarkable creature. I posted earlier about finding adult moths this summer but this morning on a 20 kilometre ride, I found a luna moth caterpillar. In northern climes such as Nova Scotia we are lucky to get one generation in a summer. In more southern climes, like Texas, they have 2, sometimes 3 generations in the longer summer season. The caterpillar I found today would have been an egg in late June, a first instar by mid July, and this morning it was in its final instar. Instar simply means stage of development as a larva. After some research on the net I was able to determine that because of its orangy/brown colour and its behaviour (it was on the ground trying to get across the path rather than in a tree eating leaves) that it was in its final instar and was probably close to cocooning, insomuch as these things cocoon. They don't make an elaborate cocoon; they simply wrap themselves in leaves using a little bit of silk to hold down the edges. If this was in Texas, the caterpillar would spend a couple of weeks wrapped up like a cabbage roll before it would become an adult moth. But because we're in a northern clime, it may be asleep til the spring. I have to check with the local museum about how to keep it over the winter, but from what I've read, I may be able to make a hammock for it to be suspended over a little bit of water, and the whole contraption placed in the fridge.

It is approximately 3 inches long, 4 when it's on the move, and it's as thick as my thumb. Its rear end has a couple of unusal markings on it, kind of like eyes, to fool predators.
I have named it Fred. Pretty, eh?
By this evening it had shown no interest in eating but I figured it was too close to cocooning anyway. I was right as by this evening, it was tightly wrapped up in some birch leaves I had provided for it. The brown spot on the leaf is right over the curled body, and you can just barely make out a little white silk just below and to the right of the spot.
What is so remarkable about this creature (actually, every creature I have come across) is how they know how to do everyting they do. It's not like they have a little handbook and even if they did they couldn't read it. They have no parent to teach them anything as the parents die before they even hatch from the egg. They are solitary creatures, so have no peers on which to rely for instruction. They are little robots that run on chemicals. Chemicals tell them when to start to shed their skin as they morph from one instar to the next. Chemicals tell them what to eat. UV light sets off chemical reactions or stops them so they know when it's day or night and they act accordingly. Chemicals tell them that it's getting cold and time to wrap up in a leaf so they drop to the forest floor to look for appropriate leaf litter.

As adults, chemicals tell the males where the females are and off they go. Chemicals tell the females to emit those pheromones and wait for a male. Chemicals indicate which leaves on which to lay eggs and sometimes, if death is imminent the female lays eggs willy/nilly, whether they've been fertilized or not.

As caterpillars these creatures are eating machines. During metamorphosis the digestive system is...well...digested, so to speak, and the adults have no mouth parts. All of their energy comes from stored fat that lasts them about a week, if they're lucky and not eaten by a bat or owl. Or caught by a curious collector.

Many species of moth have similar lifestyles, though lifestyle implies a choice. These creatures don't have a choice. They appear to be simple little flying things that annoy a few of us from time to time on the front porch, feed many birds and other animals higher up on the food chain, and sometimes take our breath away.

But it is their apparent simplicity that makes them so remarkable. Simpler and better living through chemicals.

Added Aug. 31:
I was lucky enough to have found someone on the net to help me with this project. Her page on these moths is a valuable resource for anyone else interested in reading more:
Liz has recommended an outdoor cage which I will construct and take pics of to show you before Fred goes back outside for the fall and winter.

Added September 1:
Liz has written me to correct something:

"Actually, they do make a real cocoon - it's not accurate to say they just wrap themselves in leaves with silk to hold down the edges. The cocoon is thinner than those of most saturniids, but it's completely there (wait a couple of weeks and you can pull the leaves off and see it). (Don't change the cocoon's orientation to the ground until the caterpillar has finished spinning the inside part - they spin the outside with an "out" end, and then spin the inside with an "out" end too, and then pupate with their head pointing towards the "out" ends, so when they need to hatch they can get out. If the cocoon is re-oriented halfway through the process, the larva may put the inside "out" end at the wrong end, and then have trouble escaping as a moth. It should take about a week to be completely done spinning and safe to move around.)"

How cool is that?



Um.... they sound remarkably complex to me. And that's a whole lotta chemical activity going on. Amazing really.

ps. glad you liked the cartoon.

Robin said...

Yeah, this is fascinating, but it kind of makes my head hurt.

Is the bug *aware* what it's doing? Sort of? "Robot" makes me think of some kind of little organic automaton. Which would kind of be a shame.

After all, when it's into its mating period, shouldn't it at least have enough awareness to say to itself, "Hey, this is pretty cool. I wonder what the heck I'm doing?"

Shauna said...

Most creatures are unaware of what they're doing. From a strictly biologic point of view, they are slaves to the chemicals in their bodies reacting to the chemicals outside their bodies. However, they do have the ability to learn, even bugs.

Their apparent simplicity is what makes them so interesting. There's so much more going on below the surface. I can understand why your head hurts. Mine does a little too, if I spend too much time on it.

The Wookie loved the cartoon as well...heh. Must post it here....



I kept reading about this wormy thing living in Texas and it dawned on me that I, too, pretty much liked to roll myself up in a leaf or two on a hot day and stay out of the sun when I lived in Texas!

You are pretty remarkable...

Linda D. in Seattle