Wednesday, August 22, 2012
Tuesday, August 21, 2012
Bugs & Moonshine
Regal moth caterpillars in sleeves in my front yard. In the close-up you can see them -- they are about an inch long now. I used nylon screen for my sheeting material because it's hot here in Charlotte and I didn't want them to cook, but normally any thin fabric will do.
Fill it with new made corn mash and never more you'll toil
You'll just lay there by the juniper while the moon is bright
Watch them jugs a-filling in the pale moonlight.
It was like that: vaguely weird, vaguely criminal (was shipping insects around the country through the mail legal? my dad wanted to know), and somehow beautifully lazy. It was fun riding around in the midsummer night on my bike like a bandits, collecting moths, building my stock. It was easy work tending the caterpillars – I just made the rounds every few days, checking the sleeves, letting the droppings fall out, making sure there were plenty of leaves still left. It took me no more than 4 hours a week, at least when the caterpillars were small. It left a lot of time for lying in the hammock with a book and going swimming with my buddies in the gorges.
But there were some anxieties, as there is with any entrepreneurial venture. After I first put the eggs in the sleeves, I didn’t check them for two weeks, knowing they would take a while to hatch. We had a lot of rain and I worried that they might be drowned by it. When I opened the first bag, I saw nothing, absolutely nothing at first, and I immediately thought “Oh, no – I’m going to have to send all that money back!” Then I noticed a fine powder of minute droppings at the bottom of the bag… I started gently flipping through the leaves – there were tiny black cecropia caterpillars everywhere.
Thursday, August 16, 2012
Who Cares How You Look?
The birds do, Mr. Doo-doo.
Why do they see that in this harmless little caterpillar? Well, the splotchy pattern and the squiggly curve of the body does look a bit like the dropping photo, but this is also something that they have seen before in the bug world. Here are some other examples from both moth and butterfly caterpillars:
"Orange Dog" -- caterpillar of the giant swallowtail butterfly
Moonseed moth caterpillar
Ruddy daggerwing butterfly caterpillar
Monday, August 13, 2012
Citizen Science – Not.
There are hazards to having 250 caterpillars crawling around your house…
Saturday, August 11, 2012
A Southern Strategy
The votes are in…
Well, as I said, surprise, surprise – the experiment was over almost before it began. When I gave some of the caterpillars pignut hickory (the most common hickory in our area), they clearly refused to eat it. Newly hatched caterpillars sat together on the glass walls of their hatching cage, like kids huddling in a crowd outside a classroom they don’t want to enter, and wouldn’t go near the leaves, though they were fresh and clean. After a day and a half, I began to worry that they were going to die if they didn’t eat, so I also put in some sweet gum leaves, which their earlier hatchlings had already accepted readily. Within an hour, they were on those and eating – you can see this in the picture below.
1st instar caterpillars on sweet gum leaves. Untouched hickory leaves are in upper left corner.
Though the ranges look pretty much alike (sweet gums can’t take the long, cold winter of the north and regal moths, which pupate in the ground, without insulating cocoons, probably also have an issue with cold), I notice that the range of the regal moth is somewhat larger, going a little further north than the sweet gum tree. So … northern populations of regal moth in, say, New York or Massachusetts, must eat something besides sweet gum. This may be why the books describe the other plants as known food for the moth. If the moth’s range started in the south, eating sweet gum there, and expanded north, then it had to evolve to eat other foods in order to move further north…
Tuskes, Paul M., Tuttle, James P. and Collins, Michael M. 1996. The Wild Silk Moths of
Friday, August 10, 2012
Monday, August 6, 2012
Food Loyalty in Bugs
In which I talk about picky eating in bugs, and decide to try an experiment…
Toxic monarch caterpillar on toxic milkweed plant
Plant-eating insects like moths and butterflies have evolved this way with specific plants for a long time, which makes most of them picky eaters… which is why a non-picky insect like the royal moth is somewhat unusual. How would a moth come to be this way? My best guess (another “hypothesis” of mine) comes from something that I was talking about two posts ago – the fact that regal moths and their relatives seem to be relatively recent “invaders” from the south, taking advantage of ecosystems that are relatively “new,” thanks to past ice ages. In ecology, scientists note that the species that can best take advantage of a new place (where there are not a lot of established, well-balanced relationships between species) are creatures they call “generalists.” Generalists are species that can eat lots of different things, aren’t fussy about living arrangements, etc. and thus are able to make do in new situations better than other organisms that depend on established relationships with each other. In older ecosystems where all the organisms have long worked out their relationships with each other, these “generalists” may not do as well, but in less-established situations they do better. Curiously, this points to the fact that the regal moth, apparently a relatively recent invader, is somewhat of a “generalist,” despite its unusual appearance (which looks very specialized) and freakishly large size. It’s well-suited to survive in a variety of conditions by eating a variety of foods.
The thing is, evolution is still going on. WSMNA notes that some studies have found that for regal moth caterpillars “the effectiveness of host plant assimilation varies from population to population.” In other words, regal moths in different areas appear to be evolving preferences for different species of foodplant. The authors go on to say: “A study of localized preferences in this species, with its broad array of natural host plants, would be an interesting topic for further investigation.” Suggestion accepted: I think I will attempt a small (and poorly designed, since I’m winging it) experiment.
What I am doing is picking two different foodplants -- pignut hickory and sweet gum -- and testing whether one seems in any way to be a preferred choice for the caterpillars I am raising. Do they accept one readily but not the other? Do a larger percentage survive when fed one than when fed the other? Do caterpillars grow at different rates on the different plants? (etc.) I picked these two plants because both are really common here, and both are on the list of “most common host plants.” They are not closely related plants, so they are likely to have significantly different toxins in their leaves.
Tuskes, Paul M., Tuttle, James P. and Collins, Michael M. 1996. The Wild Silk Moths of
Friday, August 3, 2012
The Caterpillars Have Hatched and They Look...
Awww... cute? Really, somewhat badass. Like they want to be punk rockers when they grow up.
Honestly, I can say that regal moth caterpillars have more "hair" (actually, they are spines) per body mass than any other creature I've ever seen. They are about 1/3 an inch long(say a little over 1 cm, if we go metric -- the largest just-hatched caterpillars I've ever seen too) and about a third of them is spine.
Why they would evolve to have such a bizarre body at hatching is anyone's guess. At this size, "protection" seems pointless, and this is an huge encumbrance, not to mention a waste of resources. I guess the "designer" wasn't so smart on this one.
Anyway, I have them started on a foodplant -- sweet gum. This is going to be my primary foodplant for both the regals and the lunas, since I have a lot of it in my yard, with plenty of branches that are within reach. I'm also going to do a little experiment, feeding a small number of the regals pignut hickory instead, but more about that in my next post. Both luna regal moths eat pretty much the same trees (a lot of different nut trees and others with aromatic leaves...) though regal has the bigger palate.
I'm going to "sleeve" these caterpillars outside soon, but when they are this small I don't want to lose any, so I'm starting them on potted saplings inside. I've made a tube of nylon screening that I can put over the plant and tie at the top for easy access. This allows the cage to "breathe" and hopefully will keep the babies from drowning in condensation drops or getting mold. A lot can kill you when you're little. I'll lose some anyway, but with any luck, not too many.
By the way, another strangeness with these bugs: A group of them hatched VERY rapidly. I looked at the eggs and none had hatched at about 9:10 this morning. I looked again just a little before 10 and there were a couple of dozen crawling around. The eggs were not laid very simultaneously, so hatching must be triggered by some kind of environmental factor -- light? Anyway, interesting. I notice that there seem to be big groups at different (but similar within the group) stages of development (judging by color).
Thursday, August 2, 2012
Imagining the Moth
My personal best guess for why regal moths have evolved to fly long distances and lay single eggs is that, since these eggs grow into very big caterpillars, it would be a bad idea for too many of them to be on one tree because they are likely to attract the attention of predators (such as birds) and once a predator has found one caterpillar, it is going to be primed to see another one nearby. So, this hypothesis says I saved the female moth the effort of flying all over the forest to lay her eggs, so she probably was able to get more laid before her fat-stored energy ran out (fat is really just a chemical battery, if you think about it). She had to lay them all together, which might be disastrous in nature where there are birds, but I’ve got her back – I’ll protect her caterpillars from predators. This makes me the good guy. Really.
Young oakworm moth (A. osalari) caterpillars. National Park Service photo by Sally King.
This is another perhaps un-provable hypothesis regarding evolution, but I like it because it again makes you expand your imagination to consider yet another dimension that can affect things: history. Consider the fact that only a little over ten thousand years ago (a blink of an eye in biological history, really) most of