August 7th, 2007
three caterpillars
On Saturday, while out for my evening walk, I checked Common Milkweed (Asclepias syriaca) leaves for signs of caterpillar feeding. In just one small area of a meadow, I was able to find three different species of caterpillars. I collected three leaves to create the above photograph (click on all photos for larger views). From left to right, the caterpillars are the Milkweed Tussock moth (Euchaetes egle), the Dogbane Tiger moth (Cycnia tenera) and the Monarch butterfly (Danaus plexippus). I believe the two moth caterpillars are probably still a molt away from being final instars, at which stage they would cocoon. The Monarch caterpillar is just a third instar, so has a couple of more molts to go before it will form a chrysalis.
If you’re interested in studying caterpillars, this is an excellent time of year to do so. Most moths and butterflies will have laid their eggs awhile ago. The resulting generation of caterpillars will be busily feeding in order to attain their full size before pupating. Smaller caterpillars will create holes in leaves, while larger ones will often eat away a good part of the leaf as in the above example. Very large caterpillars such as the Cecropia, will actually eat so many leaves that a tree branch may become conspicuously bare. That’s how I’ve managed to find them in the past — by watching for branches that are without leaves.
Some of you may remember that I recently wrote about Dogbane Tiger (Cycnia tenera) moths. They were the delicate white moths with yellow along their wing edges. Above is the larva — a furry gray caterpillar. According to this page from Wikipedia, there can be several generations of Cycnia tenera in most ranges, so caterpillars found now might cocoon and emerge this season. If I see any more, I’ll probably collect one or two to rear.
The Milkweed Tussock moth (Euchaetes egle) caterpillar is one that we frequently see around the farm from this time onwards. The one in the above photo is a final instar photographed in 2004. Notice how it has more white tufting than the caterpillar in the top photo from August 5th. Caterpillars often look quite different at each successive molt. Some species have different colours, or length of setae (fur-like covering), or they might have antennae or horns, or some other distinguishing feature. The variation between instars is one of the things that makes it a little challenging to identify caterpillars, especially the early instars of each species.
I often find the younger instar Milkweed Tussock caterpillars feeding together as in the above photo. If alarmed, the younger instar caterpillars will thrash about wildly in an attempt to repel potential predators. According to this page also from Wikipedia, there is only one generation of these caterpillars in the north This moth would overwinter in its cocoon, making it one that I won’t be collecting as I don’t wish keep any pupae through until next spring.
So, if you want to see some caterpillars, get out walking about the fields and woods, turning damaged leaves and watching for conspicuously bare branches. You’re bound to find at least one or two.
Tags: Milkweed Tussock Caterpillar, Euchaetes egle, Dogbane Tiger Moth, Cycnia tenera, Monarch butterfly, Danaus plexippus, Common Milkweed, Asclepias syriaca