The Mystery of the Donut's Hole
This scene, this conversation, must have taken place 20 years ago, maybe more, for it was back in the days when there were still hippies and I'd recently moved to the Ozarks. I was middle-aged, and an ex-librarian, but I'd made friends with some of those back to-the-landers, colorful, bewildered, engaging young people. My memory is of a warm, humid, summer evening. We were sitting outdoors, scratching our chigger bites, thinking ourselves explorers of a new world.
Fireflies flashed. Insects chirred and buzzed. Katydids debated. Cicadas whined like buzz saws. The sense of lushness, sex, potential was palpable. One young man, Cortez-silent, upon a peak in Darien - finally blurted out, "This must be the kind of place where new species are formed all the time."
Older, priding myself on what I considered to be greater rationality, and probably not high on a controlled substance, I demurred and gave a cautious lecture on the pace of evolution in which I used a lot of Latinate words.
Well, a lot of water has passed over the dam since that evening and here I sit, like some mad scientist, cross breeding camel crickets, testing out the young man's supposition.
It didn't take me long after moving to the Ozarks to realize it was a special place, but it was only a few years ago that I discovered I was living at the center of a great orthopteran mystery.
Camel crickets belong to the insect order Orthoptera. They are those hump backed, pale fawn crickets a couple of inches in length with the black stripy hind legs. They are good jumpers but don't fly and don't chirp like their cousins, the hearth crickets. They are common, harmless insects, found in one species or another all across the continent. I've been familiar with them for years and curious about them because there is so little in the field guides about them.
A few years ago I began to learn a little more. What I learned (but more importantly, what I didn't learn) is laid out in detail in the final chapter of my 1993 book, Broadsides from the Other Orders; what may be of interest to Missourians is that it turns out that a portion of the Ozarks of southern Missouri, where I have my farm, lies in the puzzling center, in camel cricket reporting data, of a species circle.
The camel crickets in that center, although of the same species, are mysteriously different. The map makes them look like residents of a hole in a donut. The species is Ceuthophilus seclusus in the maculatus group. Their name, therefore means, roughly, spotted shy crevice-lover. And having introduced one bit of Latin, I'll have to introduce another to explain the mystery of the donut's hole.
Camel crickets, like other insects, protect their bodies with a hard, tough exoskeleton covered with separate pieces or plates. These plates, depending on their location on the insect's body, have different names. The plate that extends across the back of what we would like to call the camel cricket's neck (but mustn't because it lacks a neck) from the base of its head to the top of the first part of its body, or thorax, is called a "pronotum."
Female camel crickets that live both in the rim of the donut and in its hole have a sleek, gently rounded pronotum. So do males who live in the donut's rim. And so do the males who live in the hole while they are still youngsters. But as these hole-dwellers molt and grow bigger and come to sexual maturity something strange begins to happen to their pronota. Just behind their head, an orange lump begins to swell up - bright, colorful, easy to see against the pale fawn of the rest of their body. And as it does, perhaps even to make room for it, the rest of the pronotum develops an inward fold, a notch.
Your eyes have, in a few seconds, danced across this paragraph which it has taken me a few minutes to write. But it took me a year to learn about this anomaly, three years to experiment with it, and neither I nor anyone else understands the least thing about it or what it signifies.
When I began work on the camel cricket chapter of my book I proceeded as I usually did in writing about other bugs. I took a fresh notebook and went to the Library of Congress and settled down to find out which entomologists had written what about them. I discovered that practically nothing was known about the biology and behavior of camel crickets.
Little had been written beyond the 1936 classificatory, descriptive work of Theodore Huntington Hubbell, the great University of Michigan orthopterist (alas, not a relation). It is 550 pages long and treats with one genus, Ceuthophilus. At the time I did not even know that Ceuthophilus was the genus of my Ozark camel crickets, for identification is tricky and can only be done by an expert. T.H. Hubbell, I learned, was dead and so I decided if I were to learn anything about camel crickets I would have to do so from personal observation.
I began capturing Ozark camel crickets from my farm and made a nice home for them in a terrarium. Gradually I figured out how they like to live and what they need to eat in order to thrive. Through a complicated series of events, I became acquainted with a former student of Dr. Hubbell's, Ted Cohn, now retired from the biology department of San Diego University. Ted spends part of his year working on the camel cricket collection at the University of Michigan and agreed to identify my pets.
After I sent him some killed, preserved samples of my Ozark camel crickets, he telephoned me in great excitement. He explained that Dr. Hubbell had always been puzzled by these camel crickets. They were of the same species as those just a few miles away and yet the males had notched pronota, often, at least in the older individuals, ripped and torn.
Some male insects offer females that they are courting a food gift from their own body. Did the female camel crickets, perhaps, bite into the male's pronota before mating? No one had ever seen them mate. Could I watch and see? Would females from these populations refuse to mate with males with a smooth pronotum even though they seemed to be of the same species? Samples from my area were few. Could I collect for him so that he could map the precise boundaries of the area in which the notched pronotum males lived?
I, in turn, had questions to ask him. One of the great benefits of writing my book was interviewing and getting to know a number of talented and interesting entomologists and Ted was one of them. The book is done now, but the fun goes on. I continue to work with Ted, continue to raise camel crickets, and continue to add to my list of questions about them, for each new observation on their biology and behavior generates several new questions of its own. I have enlisted the help of a number of people in my part of the Ozarks to collect camel crickets for Ted's mapping purposes (10 year-olds are best; they are patient, thorough, capable of intellectual excitement, and are, generally, badly underemployed.)
I have four notebooks filled with personal observations of my captive camel crickets. Although I have witnessed many of their wooings and matings I have never seen a female feed from the male's orange gland, if that is what it is. I suspect the pronota of older males simply ruptures from the wear and tear of life on a fragile part of the insect body. For two years running I've been cross breeding camel crickets from the rim of the donut with those inside of the hole.
Last year I isolated a virgin female from my house, one of the notched pronotum population, which I'll call "holers" from now on, and let her breed once with a local male. Then, weeks later, I mated her, also just once, with a male from 20 miles distant, one from the smooth pronotal population, henceforth known as "rimmers," a resident of the rim of the donut. The reason I had to wait so long to mate her the second time is that rimmers take longer to mature than do the holers, a situation which I find interesting and perhaps significant in helping to solve the puzzle.
The female's first batch of offspring hatched out and grew up. The males had the characteristic notched pronata with the orange bulb. The second hatch, which came along much later, was about a zillion baby camel crickets. They took a much longer time to mature than did the first hatch, corroborating my observation of the rimmers in the wild. But they had a lot of trouble growing up.
The zillion rapidly decreased in number. Many died while molting from one stage to another, trapped in their old exoskeleton; some were deformed, legless. There were many monsters in the population with abnormally thickened or distorted bodies. They climbed and jumped less than their step brothers and sisters. In the end, only two females and a single male - and yes, he had a smooth pronotum - grew to sexual maturity. They mated and the females laid eggs which were fertile and young camel crickets hatched from them.
A species is defined as that population which interbreeds and produces fertile offspring, so this cross breeding indicates that these two populations are still a single species. But it also suggests something to be tested out in later experiments: the males' genes are the ones that determine whether or not the male offspring will have notched pronota with an orange bulb. In the wild where the two populations overlap they seem to be separated by differing speeds of maturity so they would, in fact, have little chance to interbreed. Could this separation in time be the isolating mechanism that allows a new species to form?
In the spring I simplified the experiment. I segregated males and females from both populations. Unfortunately the male rimmers all died or ate one another while in vulnerable molt before I could give them to mates. I'll have to catch more next year and separate the males, each to his own jar. But I was able to bring along some of the female rimmers and presented one, mature, but virgin, to a local male, a holer, who had been mature but unmated for weeks. They mated. It is August as I write this. The male has long since died at a ripe old age for his kind, but the female lives on. I have seen her lay eggs. and I hope to see them hatch and will watch to see what kind of males are among the offspring.