A brutal fate (or why you shouldn't come back as a caterpillar)

Last Saturday, August 13, the Midwest Native Plant Society sponsored a one-day workshop on pollinators. It was well attended, with over 140 participants. The speakers were great, fun was had, and there were field trips following the indoor sessions.

The venue was the U.S. Army Corps of Engineers' fabulous visitor center at Caesar Creek Lake in Warren County. We really like holding events at this place, as the conference room is perfect for groups of up to 175 or so people, AND one only need step outside the doors to get into interesting habitat. As proof, one of our field trip leaders, John Howard (striped shirt, back to camera) shows a group a huge female Dobsonfly on the wall by the doors. There was also a stunning Cloudless Sulphur butterfly in the raised flower bed, near that rock.

At the end of the day, a couple of us were poking around the woodland edge near the visitors center when I spotted a Redbud, Cercis canadensis. As this tree is often productive for finding various slug moth caterpillars, we went over to inspect its foliage. It didn't take long before I spotted one of our most striking caterpillars, the Saddleback, Acharea stimulea. It's always a crowd-pleaser.

NOTE: The Saddleback in this photo is a proxy for the actual specimen that we found. I imaged the animal above two years ago in southern Ohio. Scroll on and you'll see why I used a substitute image to show what one of these cats looks like.

Here is the actual Saddleback that we found on the Redbud last Saturday. It's dead, and its body bristles with the cocoons of a Braconid wasp. There are so many cocoons festooning the unfortunate cat's body that it took me a minute to realize what species we were looking at. To top off the predatorial assault, there are even a few tachinid fly eggs on the body for good measure.

Braconid wasps and tachinid flies, among others, are parasitoids. Parasitoid insects such as these generally kill their hosts. One of these flies or wasps lays its eggs on - or injects them into - the victim. The eggs hatch quickly, and the tiny grub begins boring its way through the host's body, consuming non-vital tissues at first. Obviously, as evidenced by the photo above, many such larvae might occupy a host. The parasitoids cleverly avoid consuming the organs that allow the caterpillar to continue to remain mobile and thus better elude other predators, such as birds. Finally, in a grisly last hurrah, the larvae finish off the victim and burst from the dead husk and spin tiny cylindric cocoons.

It takes a few days for the wasps to pupate and emerge from their cocoons. I saw an opportunity to attempt to make images of the emergence, and took the caterpillar and its gruesome hitchhikers and placed the whole shebang in a clear vial. I tried to check on the occupants every hour or so to see if anyone was hatching. Today (August 15) was the day.

I had the vial in my office, and when I checked it around 10 am, a few wasps were flying about within. An inspection of the cocoons revealed that most appeared ready to hatch, but in spite of regular monitoring, no more emerged during the day.

I left the office around 5:15, vial and camera in hand. When I reached my car in the parking lot, I took one more look before stowing everything. Probably two dozen wasps were flying about! Perhaps my moving the vial jostled them into action, I don't know, but I rushed back to the building to create some images of the wasps emerging.

It doesn't take long for one to pop out. As the pupa matures into an adult wasp, the outer edges of the summit (lid) of the cocoon get thinner and more fragile. The wasp then apparently chews a very neat incision around the summit of the cocoon, and when the time is right, it pushes up and pops the lid off. From the time that I could detect an obvious movement of the lid in the case of the wasp above, it was probably only 30-45 seconds before it had broken completely free of the cocoon. The three cocoons to the right of the wasp still have their occupants. Other cocoons have the lids popped and we can see the almost perfectly circular shape of the lid.

Just seconds after emergence, a braconid wasp takes stock of its new world. After a brief run-around, it took wing and vanished.

Making images of these insects was not easy. The wasps are probably only 2-3 millimeters in length - smaller than can be effectively dealt with by using a "normal" macro lens such as my Canon 100 mm. Thus, I resorted to the tricky but useful Canon MP-E 65mm "mega" macro lens, which magnifies up to 5x life size. But this lens is not forgiving, and very hard to use on objects that are moving. It has no focusing system; the operator just moves the camera back and forth to focus. Depth of field is extremely shallow, even at f/16 (what these images were made at), and front of the lens flash is essential. And it is nearly essential that the camera be firmly braced in some way.

But if all goes passingly well, we can see into a micro world that is far too small to be visible to the unaided eye.

A wasp gives brief pause after a few wing shakes and a spot of grooming. An instant later it was gone. The spearlike spikes to the right of the wasp are part of the caterpillar's armament of stinging spines. Saddlebacks are said to have a very painful sting, but while such weaponry may work on birds and other larger predators, it is not effective against small parasitoid insects.

The wasp family Braconidae is immense, and undoubtedly includes scores of species as yet undescribed. I have no idea what species these wasps are, or even the genus. Identification of species in this group is the bailiwick of specialized experts, and I suspect specific identification isn't even possible in most cases without a specimen in hand. If anyone reading this can shed more light regarding identification, please let me know.

I captured this wasp just as it was ready to take wing. Note the dark stigma along the leading edge of the forewings.

A fate such as documented above is very common in the caterpillar world. Those of us who regularly hunt for caterpillars are quite used to seeing victims bristling with wasp cocoons, and/or the shells of empty tachinid fly eggs stuck to their exteriors.

Very little in Nature is Disneyesque.

Native wasp attacks emerald ash borer

A while back, I wrote HERE about the apparent spike in at least some woodpecker populations. It seems that the feathered hammerheads have found the juicy grubs of the invasive emerald ash borer, Agrilus planipennis, to their liking. Can't beat that - any native predators rising up to attack and hopefully repel the incredibly destructive nonnative borer can only be a good thing.

Yesterday, I was going through reams of photos in my Hymenoptera (ants, bees, sawflies, wasps) folder looking for images for a new project. Filed away was this image of a small but stunning braconid wasp. I had taken it last August in Athens County, Ohio. At the time, I had determined its identity as Atanycolus cappaerti (no known common name, to me), and forgot about it. Since the new project - more on that later - is all about bees and wasps, I delved deeper into this little beast.

Wasps in the Braconidae family - which is immense, with some 17,000 species so far described - are parasitoids. I've written many times about various parasitoids, which typically kill their host organisms.

As it turns out, the little charmer above goes after wood-boring beetle grubs, and has apparently taken a shine to the grubs of the emerald ash borer. Very few of our native parasitoid insects seem to have set their sights on EAB as a host, so major props to those that have, such as the exquisite Atanycolus cappaerti.

The animal in my photo is a female, evidenced by that long "stinger" projecting from her abdomen. The needlelike structure is actually an ovipositor, and she uses it to auger through tree trunks and into EAB grubs, into which she injects an egg. The egg soon hatches, and the emergent wasp grub begins eating its host. Native wasp - 1; nonnative borer - 0.

There are reports of Atanycolus population spikes in areas of EAB infestation. Let's hope that trend continues, and the native wasps help to eventually bring the uber-destructive pest under control.

Some gorgeous little bugs

Lots of bugs this weekend. Saturday night, I gave a program about "singing insects" - the Orthoptera - at Dawes Arboretum. We limited it to 25 people, and had a full house. After the presentation, we headed out into the dark and I've never had such luck finding cool bugs. Right off the bat, we tracked down and captured a Slightly Musical Conehead, the first of many. A Greater Anglewing was singing from the roof of the building that I gave the talk in. Restless Bush Crickets put in multiple appearances. And on it went - the best nocturnal singing insect foray that I've yet done.

 

Today, Jess Henning and I made a whirlwind trip into the backwoods of Athens County to check out a few spots, and encountered lots of noteworthy plants, and insects. I of course had the camera in tow, and managed some decent images. Following are a few of those...

 

A Snowberry Clearwing, Hemaris diffinis, works the flowers of a Rough Blazing-star, Liatris aspera. The dry meadow where this moth was found was full of blazing-star, and various pollinating insects. Shooting the hummingbird moths is a challenge, as they are in more or less constant motion, and their wings are a blur. When I encounter one and begin the hunt, I flip my camera's settings to shutter priority, and jack the shutter speed WAY up in order to better freeze movement. This image was made at a shutter speed of 1/2,500, with no flash.

A female Zabulon Skipper, Poanes zabulon, was also working the blazing-star. I must confess to largely ignoring the small skippers, and appreciate George Sydlowski for correcting me on its identification.

My favorite shot of the day. This is a TINY braconid wasp, and I think it is a species in the genus Atanycolus. It's a female, as evidenced by the long spikelike ovipositor protruding from the rear of her abdomen, and the entire animal was probably only 5-8 millimeters in length.

Braconid wasps are parasitoids of various insects, and species in the genus Atanycolus go after the grubs of wood-boring beetles. She'll somehow divine the location of a larva deep in a log, and auger that long ovipositor down to it, and lay an egg or eggs on the victim. The newly emergent wasp larvae will bore into their host, and eat it.

Don't come back as a caterpillar

What a day yesterday was. After attending a conference all day in downtown Cincinnati, I hustled off to meet one of Ohio's preeminent herpetologists. He showed my what is now the Queen City's most famous reptile, and I've got photos of that excursion to share later.

Following that, it was off to Adams County and the Edge of Appalachia preserve for an 8 pm meeting. Why so late? Caterpillars. We had enticed a major newspaper to do a story on caterpillars and their importance to the environment, and as most caterpillars are active nocturnally we had to adopt an owl's schedule. Thanks to whiz-bang naturalists John Howard, Rich McCarty, and Mark Zloba for agreeing to help the reporter and photographer find some cats and learn about their fascinating habits. I'll share more about the article once it emerges.

John, Mark and Rich had been keeping a watchful eye for caterpillars all week, and capturing various interesting ones. By doing so, we'd be assured of having lots of interesting goodies to show off, should our nighttime search efforts not bear much fruit. This is one of the cooler cats: a spotted apatelodes, Apatelodes torrefacta. Apatelodes are common, and generalists that feed on the foliage of a wide variety of common trees.

As you've noticed, this silky cat is heavily beset with long setae, or hairs, and looks like a tiny, tubular Pomeranian dog. There are probably two primary reason for all of the "fur". One, it makes it tougher for birds to snack on Apatelodes, as all of those bristles are unpalatable and it's just not worth the bother for most bird species. Two, all of the hair may make it tougher for the parasitoid insects - flies and wasps - to get at the caterpillar's body and attach their eggs. And as we shall see, the latter fate is a caterpillar's worst nightmare come true.

As we moved through the dark forest, searching the plants with lights for foraging caterpillars, John Howard spotted this spectacle. It is a large sphinx moth caterpillar, covered with the coccoons of braconid wasps.

The Braconidae is an enormous family of parasitoid wasps - some authorities believe there are in excess of 100,000 species worldwide - and we've got scores of them in Ohio. A parasitoid should not be confused with a parasite. The latter is something like lice or ticks. They're a bother, and they take from their host, but they don't kill it. Parasitoids such as braconid wasps ultimately kill their victims.

The female wasp has a long stingerlike ovipositor, and she uses it to inject eggs on or into the tissue of the caterpillar (or other insects, depending on the species of wasp). Along with the eggs comes a special cocktail known as a bracovirus, which serves to infect the caterpillar's immune system and mask detection of the invading eggs. Once the wasp grubs hatch, they begin feeding on non-vital innards within the caterpillar - eating it alive, essentially. It is in the wasp grubs' best interest to keep the caterpillar alive as long as possible, so they have fresh food to see them to maturity, and also a living caterpillar is better able to hide and avoid other predators such as birds.

Finally, when all is ready, the wasp grubs burst through the skin of the caterpillar and form the cyclindrical little coccoons that we see in these photos. Amazingly, this caterpillar was still alive, although barely. Perhaps even by now, a day later, the wasplets have emerged from their coccoons, leaving the dried husk of the sphinx caterpillar. A seemingly terrible fate, but one shared by scores and scores of caterpillars.