Saddleback bites the dust

Not long ago, I was delighted to come across a small redbud tree filled with caterpillars. There were at least five species noshing away, including three saddleback caterpillars, Acharia stimulea. Saddlebacks grow up to be rather ordinary little brown moths, but they're truly spectacular as larvae. It's as if a sea slug was saddled with a tiny lime-green horse blanket.

However, I noticed that the individual in these photos was not looking especially lively. Even though the caterpillar looked pretty good - slightly faded, perhaps - something was amiss. So in we go for a closer inspection.

Uh oh. While making macro photos - those little columns of spines will give you one heckuva sting by the way - I noticed a major problem for the poor little cat. That tiny white cylindrical object is an egg from a tachinid fly. These bristle-bodied parasitoid flies are among a caterpillar's worst nightmares. In this case, I think that's probably the old case of the egg - as we shall see, it looks as if the fly has already spun its gruesome magic.

Tachinid flies, which rather resemble house flies, are major caterpillar predators and attack the cats by sticking an egg to the the larva's exterior. In short order, the fly grub hatches from the egg and bores directly through the caterpillar's skin and into its interior.

Once within the caterpillar, the ever-growing fly grub begins consuming non-vital hemolymph fluids and tissue. Clever parasitoids that they are, it would not behoove the grub to kill its victim until the last possible moment, as a living host is better able to move about and better avoid other predators such as birds. In a final frenzy, the fly grub goes ape and eats all of the innards before bursting from the caterpillar and going off to pupate.

In this photo, we can clearly see what must be the grub's exit hole. What a show that must have been, and I'm sure you wish I had caught the grub bursting from the caterpillar's husk on video so you could enjoy that bit of cinematic loveliness as you ate your breakfast. But such a video was not to be - I suspect that these tachinid fly grubs tend to emerge under cover of darkness.

As I was making these photos, this tiny chalcid wasp alit on the caterpillar husk and began looking around. This little wasp is looking to parasitize the fly by laying eggs on either the fly grub or its puparium. The world of parasites and parasitoids (the latter generally kill their hosts) is truly strange and multidimensional.

I made this photo a few weeks ago. While photographing this caterpillar - a yellow bear, Spilosoma virginica, I believe - I noticed a tachinid fly perched nearby. The fly watched the bristly caterpillar's every move, occasionally shifting position to get other viewing angles. Yellow bears are heavily beset with stiff hairs, and the fly was undoubtedly waiting for an opportune moment to get at some unprotected part of the caterpillar. I watched for a while, but had to leave before the fly moved in. I wish I had had the time to stick around and film the actual attack.

Some cute, and not so cute, flies

I must confess to being a closet fly enthusiast. Until recent years, I never gave them much thought nor paid them much mind. Probably, like so many others, I labored under numerous misconceptions: they're ugly, dirty, trash-seeking, and boring.

Nothing could be further from the truth. The Fly World is filled with diversity and and fascinating behavior. They're endless fodder for intellectual stimulation, and make for beautiful macro photography subjects. On a recent trip to Shawnee State Forest, I turned my lens to a few flies...

A tiny flowerfly, its eyes endlessly deep pools of blood-red, wallows in a sea of buttercup nectar. This one was small enough to be measured in millimeters, like a robust gnat. A great number of fly species are vital pollinators of our flora, possibly THE biggest group of pollinators.

Many flowerflies mimic the bad guys. They resemble - sometimes to an eerie degree - wasps, bees, hornets, etc. But you can tell they are flies by the huge eyes, greatly reduced antennae, and the one pair of prominent wings (the others have two pairs). Check out this post by Eric Eaton, which features a few thick-headed flies. They mimic wasps to a remarkable degree.

This one might make you jump, should it unexpectedly buzz into your face. It's a flowerfly that's doing a mighty respectable job of looking like a yellowjacket or some other nasty stinger. There are a number of species, and genera, that resemble this guy and I'm not sure which one it is. That holds true for all of the flies in this post. If anyone does know their specific identity please let me know. I'd love to learn more about them.

This flowerfly, happily chowing away on pussytoes, was very cool. It reminded me of a potter's wasp with its stripes of white on a black body. And to further the ruse, it constantly twitched and arched its abdomen, just as a wasp does.

Here we have, I believe, a tachinid fly. They look rather menacing, and are. A lot of tachinids - and there is something like 1,900 species in North America - resemble exceptionally ugly house flies. You can tell them by the thick, coarse hairs that bristle from the abdomen. Tachinids are parasitoids; they lay their eggs on hosts such as caterpillars, katydids, or ther insects. The fly grubs then proceed to feed on the living host, ultimately killing it. CLICK HERE for a post mortem of a rare pink katydid that fell victim to a tachinid.

A particularly ferocious tachinid (I think) awaits victims. If you tune your eye to the insect world, you'll begin to notice the staggering number of parasitoid flies and wasps that are out there. They often seem to sit patiently and vigilant, carefully watching for prey. Some of them, especially the wasps, actively patrol the vegetation, searching out victims. Given the magnitude of the army of parasitoids lurking out there, it seems a miracle that any caterpillar or cricket ever makes it to adulthood.