I picture pilots jamming radar by dropping tinfoil in World War II. “How come the moth didn’t try to escape?”
“Because it didn’t have a damn thing to worry about. Instead of fluttering in the web, it lets the spider do the work.”
In the sunlight, this golden-web spider’s shimmery silk stands out brightly. Touching one thread with his fingertip, Tom pulls it farther and farther to show how it can stretch. A spider spins different kinds of silk for different parts of a web; stretchy threads have more water in them. The silk at the center of the web is so elastic that, when an insect falls in and flails, it’s essentially kicking against rubber bands. A struggling insect never really puts tension on the web; it just wraps itself up tighter.
“The elasticity of these threads is unbelievably mysterious,” Tom says admiringly. “There isn’t a single human synthetic material that has that kind of elasticity. It’s better than rubber, and the toughness is out-of-sight.” He plucks at the silk.
“Why isn’t the spider running down to your forceps?”
“A big movement like that? She knows exactly what fight to pick. And she has all sorts of strategies. If I touch the web too hard, she has lots of escape routes and will know just where to go. But I don’t want to freak her out. She’s a nice little gal.”
Nearby, a small white orchid hangs from a branch. Everywhere one turns are curiosities involving insects. Many species of orchid almost never produce seeds and even act as if they don’t want to be fertilized; they don’t produce any nectar to seduce an insect. On rare occasions, though, an inexperienced insect may stumble into one by mistake and smear pollen around. Then the orchid produces thousands of seeds, and in that hit-or-miss way it survives. Nectar is cheap for a flower to make, and yet hundreds of species of orchids are unappetizingly dry. It’s a mystery how they survive in a relationship that relies so much on accident. But somehow they manage, thanks to the bumbling of insects.
Experiments must be repeatable and include a control group, so Tom has brought two flavors of ornate moth—a naturally poisonous one (it gets that way because its caterpillars feed on a deadly variety of pea plant) and a harmless one raised on poison-free food. Time after time, the spiders devour the safe moths and release the toxic ones. When we’re content with the evidence, we head back to the station to get a second opinion from equally picky eaters—the endangered Florida scrub jays.
Back at camp, Tom adjusts the focus on a large gray Wild microscope set up in the laboratory room of his cottage. “Romance,” he says. Although there was no spoken beginning to the sentence, he concludes the one unfolding in his mind: “… and deceit.”
The insect world is storied with seduction, deception, and death. When he passes a moth to me, I hold it under the microscope and peer at its beautiful pattern. Suddenly two pinkish-yellow feather dusters unfurl from its rear end.
“Amazing! What are they?”
Tom takes a look. “Scent brushes,” he says. “Males use them in courtship. They’re actually modified scales, and each one is hollow and perforated.”
“Like a straw?”
“Very much. Vapor rises up each of the hairs on the brush. One day I saw one of these guys fly into a spiderweb. I knew that moths usually flutter themselves loose, leaving some of their scales behind, but this moth simply folded its wings and played dead. The spider came up, touched it, cut it free, and it fell to the ground. I didn’t think much about it. Then a year later I saw exactly the same phenomenon, and I decided I’d better take a look at the moth. I found out that as a caterpillar, the moth feeds on a poisonous pea plant. So I tried to see if I could raise the caterpillar on a synthetic, poison-free diet, and it worked. We knew that the pea plant had a certain type of alkaloid that is very toxic to humans. Every once in a while cows browse on these plants and die. It’s a liver poison, really bad stuff. Comfrey tea, which I don’t think is used anymore, had the same poison in it. But this alkaloid turns out to be distasteful to spiders. Any animal that can feed on these plants with impunity has got it made, because it can build up a storehouse of poison in its own body and use it for defense. And that’s the strategy of these moths.”
“So they consume it, and it saturates their body. Why don’t they die from it?”
“Great question,” he says excitedly, his voice making it clear that in his private vocabulary, “question” means the same as “puzzle.” “It turns out that when you eat these chemicals, you don’t actually eat them as poison—you eat a chemical your liver converts into a poison. And that needs certain enzymes. I think what the moth has done is shut off that kind of enzymatic system so it can take these chemicals in and not convert them, and thus use them the same way the plant does. That’s really very clever.
“So out we came with moths raised on a poison-free diet. We spent the whole damn winter raising these moths. We wanted to see whether they would be palatable to spiders. We threw them in spiderwebs, and one after another they got eaten by the spiders. I felt as if I was seventeen, on my first date, and had just got my first kiss. It was mind-boggling.
“Then I decided to look into the courtship of the moths. We knew that the males have these nifty scent brushes that they pull out for courtship. And we knew that the females attract the males. The female sits on the plant, and the males hover and fly very slowly in one direction. If you follow their line of flight, you can find the female moth that does the calling.”
“How does this siren moth call? With scent?”
“She makes an aphrodisiac in a special gland in her abdomen. I gave extracts from those glands to Jerry Meinwald, and in due course Jerry and his people came up with a formula. Actually, there are three compounds in there, all simple hydrocarbon straight-chain molecules with little bonds in them, all sex attractants. We sometimes take that chemical and put it out in traps to bring in males. This is not a long-distance attractant, but it doesn’t need to be. A few yards is all that’s needed, since a moth may spend its entire life in or near one plant.
“When the male is in range of the female, fluttering around her, those brushes come out in a fraction of a second—once, twice, three, four times as he flies around her,” Tom says, making a slow circle with one closed hand, which he opens slowly to mimic the unfolding brushes. “But there was one question that bothered me in particular. I wanted to know who was in control of this courtship. Was it the male? If so, then it was a case of metabolic expedience. The male has a useful chemical, some of which he uses for defense; the rest he converts into a chemical that works to seduce the female. Sounds good. But suppose instead this was really a female choice.”
“You mean he would advertise how much defensive chemical he has?”
“That’s exactly what ended up being the case. And I remember the moment that occurred to me. I was feeding otters in California. A question was bothering me: Was there some subtle thing that the moth could accomplish by using a derivative of this alkaloid? And the idea came to me that this wasn’t a case of seducing the female at all. It just looked like seduction. It was in fact that the male had to prove his worth to the female in some way. It was the female who was choosy.”
“So she wants a warrior?”
“She wants to have some evidence that he’s worth his salt, or whatever the insect equivalent is.”
“But he’s proving he has enough defensive chemical to protect him.”
“That’s what I thought at first, that the male was flexing his muscles, saying, ‘If you take me as your husband, your sons and daughters are going to be good at getting a lot of alkaloid out of the plant. The more they have of it, the better defended they’ll be. And this will make them better able to compete with other larvae on the food plant for seeds. And wouldn’t you like to have a suitor who can prove to you that he is genetically fit?’ Well, we published that interpretation, and we were very proud of ourselves. But then the story got even better. We found that the egg of this animal also has alkaloid in it. So we assumed that the female actually
laid eggs with alkaloid. But how does it get there? The male must transmit some of this stuff to the female with the sperm.”
Male insects often ejaculate vitamin gifts into the female along with their sperm, to make sure the offspring will have nutrients on which to grow. I remember being able to feel those ball-bearing-like packages in the soft bellies of pregnant monarch butterflies when I was tagging them in California. Insects produce some of the largest sperm packages in the world relative to their body mass. There are male beetles that donate as much as 10 percent of their body weight.
Turning away from the microscope, Tom warms to the telling of his Kiplingesque story. “Well, it turns out that the females say, ‘Look, I’m putting all the yolk into these eggs. What are you going to do for your offspring?’ So we thought maybe the male was in effect saying to the female, ‘Not only do I come from a lineage that’s good in competing for the seeds from the food plant, but I’m also willing to give you direct payment in the form of a gift with which you can enrich your own defenses, or you can put some of it in your eggs to protect them, or both.’ And that turned out to be the case. The amount of alkaloid transferred by the male to the female is proportional to the amount of alkaloid that the male has, which is in turn proportional to the amount of scent that he produces on his scent brushes. In other words, he really is telling the female exactly how much he’s got in his bank account.”
“Call me a cynic, but why wouldn’t it be in his best interest to lie?”
“You tell me. Of course, we can’t say categorically that some don’t lie. For example, if a male has very little alkaloid, could he convert it all to the scent message on the brushes and dupe the female into thinking that he has a big bank account? In theory, I suppose. But they really don’t appear to be lying. And if they don’t appear to lie, it can only be because it doesn’t pay off. They must get found out in some way. The next question in this courtship drama is how they get found out. Is it possible that the female might be able to check after mating if he was a liar, and discriminate against the sperm? We don’t know.”
“It sounds as if only the muscle men win in this scenario.”
“Not always. At one point, we released males into the field (just like the ones you saw with the spider today). Some had alkaloid, some didn’t—in other words, some with scent on their brushes and some without. We wing-notched them all so we’d recognize them; baited them with sexy females we knew would start broadcasting at a certain time of the night; convinced the females to sit on a little wire perch, which we treated chemically with an extract of the pea plant to make it more attractive for them to sit on; and then waited. A male would come in and court. We recognized the male by the wing-notching, so we knew whether he had alkaloid or not. Males with the alkaloid had about a thirty-percent higher chance of being accepted. That’s a major edge. If you have a thirty-percent higher chance of fathering offspring, that’s quite an advantage. But it’s not that the ones without alkaloid got turned away. The female can get sperm from the male, but she also has to take a big gamble and ask herself, ‘Is this the last male I’m likely to attract in the next five days? What do I do?’ At the very least, she can get nutrients from a sperm package. So she mates with up to thirteen different males, gets nutrients from all of them, and also tries to mate with as many of the ones who’ll give her the alkaloid defense as possible.”
How does she carry around all that booty, I wonder. “Doesn’t she get awfully heavy?”
“Yes. But she’s also laying eggs.”
“So she’ll be inseminated, lay eggs, be inseminated, lay eggs?”
“Lay some eggs. In fact, we know that if she gets inseminated by two males, she doesn’t lay half the eggs from the first male, half from the second. No, she will lay eggs from one male only. After mating she’s still putting the male to the test in other ways. The eggs will be sired by the largest stud. How does she tell the largest stud? Probably from the size of the sperm package. It’s mind-boggling. And the interesting thing is that the size of the male is proportional to the amount of the alkaloid he carries. It’s truth in advertising. So before mating she’s asking him, ‘Hey, how much alkaloid do you have?’ And after mating she’s double-checking him on the size of the sperm package.”
“Just leafing through the bills, to make sure all the fives and tens are there?”
“Exactly.”
Over a hundred years ago, Darwin was speculating about intrigues like this one, which involve female choice and sexual selection. He wondered if, since the female really puts so much investment into the offspring, she might not be the choosy one.
“The male strategy, almost always, is to inseminate as many females as possible, without paying much attention to them. But there are some exceptions. For example, I once worked on a beetle that ejects the equivalent of half the weight of the eggs that the female will produce. So it’s really a major contribution. And sure enough, the female has a way of conning something from the male—a gift—and then not letting him inseminate her. This female can’t mate more than once every so many days, but she tries to get gifts from males anyway. A male doesn’t want to give her gifts if she’s carrying another male’s offspring. So he goes around to the rear end of the female, which she tries to prevent, and smells her to see if she’s a virgin, something he prizes very highly.”
“What a complex courtship.”
“People have this idea that human predicaments are too complicated for an insect. Nonsense! There’s an enormous amount of biology you can pack into something the size of an insect. The only reason we know so little about them is that they’re so small.”
“I wonder how people would respond to insects if insects were larger—say, the size of dogs and cats.”
“It all depends on whether people grew up with negative ideas about insects. If the world was full of huge grasshoppers, leaping around at the speed they actually do, carrying the momentum that they do, they’d be bloody hazardous. I tell you, suits of armor would still be very fashionable. Moms would say, ‘Don’t forget your suit of armor, dear—the grasshoppers are out!’ ”
The ornate moth saga is one of Tom’s favorites. He’s been studying its habits for twenty years and always discovering something new. Although he’s usually working on a number of insect stories—sometimes just by being alert to them—one theme running through them is female choice.
“Is it possible to study insect societies and not extrapolate to humans?” I ask.
“I’m a dyed-in-the-wool sociobiologist,” he says, laughing. “It’s not surprising to me that much of what the human animal does can be described in animal terms.”
“Like giving big engagement rings?”
“Sure. Our whole courtship story can be told romantically, of course—clothing it in cultural traditions, if you wish—but the fundamental biology is that individuals are trying to perpetuate their genes in the next generation. The female is fundamentally choosy, which makes darn good sense if you’re going to sit on an egg for nine months. The male doesn’t want to waste his seed, as they say in the Bible.”
“So she tests him in various ways.”
“Absolutely. And that gets built into the culture—the whole idea of the athlete, the winner, the contests, the warrior. I can’t explain it all, but I have absolute faith that biological thinking is at the root of everything we do as humans.”
“Sometimes people think of insects as cold-blooded automatons. Comparing any of our actions with theirs then becomes doubly frightening.”
“The concept of free will is so fundamental. Do we have free will or don’t we? I don’t worry much about that, because I’m so absolutely fascinated by entering the world of another species and trying to figure out what they do. As someone who is not religious, who doesn’t believe in free will in the traditional way, who believes in evolution, and that we’re part of the evolutionary process, I still consider us to be unique in the sense that we can sit here and talk about it and understand it. But we’r
e clearly not unique in terms of what we do with our muscles; we’re not unique in what we do with our gametes when we’re mating; we’re not unique when we’re part of a courtship strategy that involves female choosiness. In those ways, we’re just animals of a different sort, ones with four fewer legs than insects.”
A knock at the door summons us, and we see a tall, chestnut-haired woman in a sweater and pants standing next to a man of about the same height, whose hair is tied back in a pony tail. Tom introduces us, and I’m delighted to discover they’re the nature photographers Susan Middleton and David Liittschwager, who are busy locating and photographing a host of endangered animals and plants. On a three-year journey around the United States, they are visually cataloguing our vanishing life-forms. Tom is looking forward to studying the grasshopper we found this morning, but he’s also excited that Susan and David will record it for posterity.
“We’re on our way to shoot some jays,” Susan explains. “We found a great spot yesterday. Want to drive out with us?”
“Absolutely!” Tom says. “Let me grab some moths. Oh, by the way,” he adds excitedly, “we’ve got the grasshopper for you.”
Susan and David cheer, and start planning their evening’s work as I help Tom pluck live ornate moths from a cage and tuck them, all silk and flutter, into separate vials. Then we climb into the Land Rover and head for the end of the station. David drives with a slightly maniacal grin; when the road becomes a river of deep, wallowy sand, the four-wheel drive is all slither and swerve for fifteen minutes.
At last we park in a maze of dwarf oak trees and clean white sand. Because the trees are roughly at eye level, it is like wandering through a scene from Shakespeare—you hear voices but can’t see the speakers, and they, in turn, don’t know you’re there. All around us, the Florida scrub is picture-perfect, even if its name suggests that it’s useless, disposable land. The scrub is an area that has deep, sterile sand. Fire and soil forge an elemental relationship that has survived for ages. One of its attractions is that, in so simple a landscape, the concerns of organisms are easy to spot. Although sand is at its heart, it’s like other simple habitats elsewhere. New York City, for example, has a lot of wild plants and insects caught between two millstones: the concrete and the unrelenting human activity. Those insects are interesting because they’ve coped with overwhelming environmental factors. Life in the scrub is similar, chastened by the tremendous sterility of the area, the lack of water in the winter, and the fires that sweep it over and over again, century after century. Many of the insect species came originally from savanna areas around the Gulf of Mexico at the end of the Pliocene, along with all sorts of antelopes, giant gophers, tortoises, and ground sloths. Many of these animals died out elsewhere, but on the scrub ridges, where the sand is deep and sterile and dries out fast, western creatures survived. So the scrub has become a home to organisms that are very old and strange. Now they remain only on the tops of a few ridges. The scrub itself is endangered. All we have left is the Atlantic coastal ridge, which is much younger than this inland ridge; Lake Wales ridge; Marian uplands; a very thin band of scrub in the Panhandle; and little knolls of scrub in small areas in western Florida. A tiny bit of Panhandle scrub works its way into Georgia and Alabama, but scrubland is almost totally Floridian. And there are many creatures unique to the Florida scrub.
The Rarest of the Rare Page 21