Lepidopterans

As much as I initially resisted the idea, the most appropriate topic for me to choose for this post is insect life.  I know—I wrote about bugs around the same time last year.  But the cyclical patterns in nature have ensured that, once again, late summer has been filled with insects—a boon for the birds, who are presumably filling themselves up in preparation for migration.  Maybe the bird migration will provide material for a few more posts this year.  We’ll see.

I don’t mean to depreciate insects, though.  To be fair, if you’re at all interested in observing birds, chances are that, sooner or later, you will find yourself paying attention to insects.  For example, the presence of tent caterpillars in an area generally prompts me to keep a look out for Yellow-billed Cuckoos, since they are one of the major predators of these rather pestilential and unsightly critters.  (Most other animals can’t deal with all of the hairs on the caterpillars.)

A tent caterpillar shelter

In a more general way, insect ecology is pretty strongly tied to patterns of behavior in birds, to the point that some bird species are declining as a result of many insect species emerging earlier in the season than they used to do.  As it turns out, warmer springtime temperatures caused by human-driven climate change can alter the timing of the life cycles of insects, and quite a number of avian species have a hard time adapting quickly to those changes.  This can be particularly damaging to nesting birds, since many of them rely on new insect broods as a food source for their young.  Fat, juicy, protein-rich caterpillars tend to be especially tempting to nesting birds, and, fortunately, it seems that there are good numbers of them in the neighborhood where I live, along with the adult forms: moths and butterflies, Order Lepidoptera.

Although nonnative plants—which tend to attract very few native insects—dot this landscape, there are still enough native species to appeal to a wide variety of bugs.  Large silkmoths, such as this promethea silkmoth that I found in late July, generally utilize hardwood trees—or, at least, their larval forms do.  Adult silkmoths have only vestigial mouthparts and are unable to feed.  The caterpillars hatch, eat leaves (which, for the promethea silkmoth, may include those of sassafras, tulip-tree, spicebush, or ash) for several months, pupate, emerge as moths sometime in the following summer, breed, and die.  I sometimes find it interesting that I ever manage to see the adult giant silkmoths at all, given how brief their existences are.  Promethea silkmoths are odd in that the males are diurnal, their activity overlapping with that of the nocturnal females only during the early evening.  The moth in my photo was a female, as the pinkish tinge of its wings indicates.  Male promethea silkmoths have very dark wings, apparently in mimicry of the toxic pipevine swallowtail butterfly.

Female promethea silkmoth

As an aside, I actually seldom see pipevine swallowtails in the neighborhood (probably because of a lack of pipevine), but I do frequently find another lepidopteran that mimics them: the red-spotted purple!  Red-spotted purple butterflies are far more closely related to another famous mimic, the viceroy (which resembles the monarch butterfly), than they are to swallowtails.  Apparently, red-spotted purple caterpillars feed mainly on black cherry, willow, and birch, all of which are pretty common in this region.

Red-spotted purple butterfly

Here’s another silkmoth—a male io moth.  The nocturnal io moth, like the promethea moth, is strongly sexually dimorphic.  Female io moths are larger and browner than the canary-colored males.  Although you can’t tell in this photo, the underwings of io moths have enormous owl-eye markings.  This species uses a wide variety of host plants, including cherries, maples, willows, poplars, and elms. 

Male io moth

What about moths other than silkmoths?  Well, one of the most conspicuous species around here is the catalpa sphinx.  The larvae, catalpa worms, feed voraciously on their host plants—no prizes for guessing what THOSE are.  

Catalpa sphinx larvae, or catalpa worms

You might have noticed that catalpa worms look somewhat similar to tomato and tobacco hornworms, with their fleshy, green bodies and spiny “horns.”  They’re all in the same family: tomato and tobacco hornworms turn into five-spotted hawk moths and Carolina sphinx moths, respectively.  The adult catalpa sphinx displays subtler patterning than some other sphinx and hawk moths, but it’s still an attractive animal.

Catalpa sphinx caterpillars strip the trees nearly bare in an astonishingly short amount of time.  This photo was taken on July 27:

Less than a week later, the catalpa tree looked like this:

August 2, 2018

The sphinx larvae clung to the veins of the leaves; they had eaten practically everything else.

The “worms” are gone now, having pupated underground.  It’s possible that they may emerge as adults to lay eggs before the summer is over, but it’s been long enough now that I suspect they will stay dormant until next year, as later broods typically do.  Update: Actually, as it turned out, there was one more brood after the one in August. 

By August 15, the tree was well on the way to recovery -- new leaves were present.

Unlike most species of sphinx moths, bagworm moth larvae remain above the ground to pupate.  You may never have noticed adult bagworm moths, but you’ve probably seen their shaggy cocoons (i.e., their “bags”) hanging from the branches of trees.  Below is a photo of an evergreen bagworm pupa on an eastern red cedar tree.  In my opinion, the life cycle of the bagworm moth is more than a little bit disturbing.  Females pupate but never develop wings, instead remaining in their cocoons as caterpillar-like adults.  They emit pheromones to attract the relatively normal-looking, winged males for mating, and then, after breeding, they die in their cocoons.  The larvae hatch inside the females’ dead bodies and work their way out during the spring and summer. 

Bagworm

Tent caterpillars, so named because they create massive shelters out of their own silk, represent yet another interesting group of lepidopterans: the snout or lappet moths.  As I mentioned earlier, tent caterpillars are frequently viewed as pests.  After all, the larvae form enormous colonies and eat several times a day.  Tree defoliation inevitably occurs, but, to be fair, the caterpillars seldom cause permanent damage.  Given that eastern tent caterpillar moths produce only one brood a year, and that the adults—the moth phase—live for only a short time, I think that we should strive to keep things in perspective.  At any rate, if having tent caterpillars around means that I will see plenty of Yellow-billed Cuckoos, then I can live with that.  As you can see in the pictures below, tent caterpillar colonies have sprung up all over the place this year.

Of course, this is by no means meant to be a comprehensive essay on southeastern lepidopterans!  Far too many species exist for me to even begin to do justice to them, and I mainly just learn about and research them as I encounter them.  If you haven’t given them much attention before, though, maybe you’ll feel inspired to seek some out this year or next.