Life Everlasting
Page 3
This mechanism for an instant color change, although perhaps known, had not been described in the scientific literature. But what was its significance? What could it be for? The color-change mechanism was unique to this species, and because it hid the bright orange, it helped make N. tomentosus a convincing mimic of a bumblebee in flight, which suggested an interesting function.
Most of the forty-six or so species of North American bumblebees have black bodies marked with yellow pile. Seven of these species also have varying amounts of orange, but that color is always bordered by yellow and is never in sharp contrast to a black band, as in the burying beetles. When N. tomentosus are flying in late summer, there are usually numerous worker bees of up to seven black-and-yellow species (Bombus affinis, B. vagans, B. bimaculatus, B. sandersoni, B. impatiens, B. perplexus, and B. griseocollis) that have nearly identical color patterns and are difficult to differentiate. With its elytral flip, the airborne N. tomentosus becomes, in an instant, a credible mimic of any or all of these bumblebees. Few birds will tackle a bumblebee because of the risk of being stung in the mouth. Unlike most other sextons, N. tomentosus can thus fly in the daytime and search for carcasses that other sextons must hunt for in dusk or under cover of darkness.
Note: pictures not to scale (except top beetle vs. bee)
Two of the common species of burying beetles that use small animal carcasses, showing Nicrophorus tomentosus (left) and N. orbicollis (right) in flight and on the ground. In both species the wing covers (elytra) are twisted, unlike those in other beetles: the undersides of the wings become dorsal and hide the bright upper sides, so that the animal in flight mimics the common yellow bumblebees.
Most burying beetles can appear to mimic bumblebees simply because they are in the same size range and therefore hum like them in flight. But N. tomentosus has gone a giant step further by acquiring yellow fuzz on its thorax and by evolving yellow color on the underside of its wings (in museum specimens the colors fade). I examined the colors of the wing undersides in fresh specimens of the other three species that I captured at the rooster carcass. None of them were lemon yellow, although defodiens was orange-yellow; orbicollis and sayi were grayish or dirty white.
This wing-cover flip mechanism probably also explains the anomaly of the mites I had seen on the back of the beetle the moment it landed. While the beetle was in flight, they had been attached not only on the thorax but also “under” the elytra, a logically safe spot to be, and had not yet changed position at the moment the beetle landed and reversed its wing covers to show once again the orange markings on black.
Details of the wing-cover twist of an N. tomentosus before taking off in flight and on landing, and (center) one of several bumblebee species that occur concurrently with the beetles. The sequence shows the color change from orange and black (three lower beetles) to yellow (three top beetles) in flight
THE IDEA OF watching burying beetles as an interesting activity was probably passed down to me by my father. And about twenty years ago I shared this interest with my older son, Stuart, then ten, who was staying with me at camp. I remembered his excitement, which I had written about in A Year in the Maine Woods. So I consulted that book (page 256) to find that we had put a dead deer mouse on some sawdust in back of the cabin “to see if a beetle would bury it.” When we checked an hour later, the mouse was gone, but Stuart found where it was buried and dug it up. I then put it at a new place, and this time Stuart sat down to watch. What he saw and said surprises me now. He saw one beetle alternately digging and staying stationary while elevating its abdomen (dispersing scent to attract a mate). Then, seeing another beetle fly in, he declared that “it sounded just like a bumblebee and I saw it with its wings still open just after it landed. It had gold fuzz on its back just like a bumblebee.” I now know that the “back” he refers to was the yellow of the overturned elytra covering the black abdomen. At the time I probably thought he was referring to the beetle’s head and thorax only. Seeing with a child’s eyes is seeing without preconceptions, and it is also, when associated with knowledge, the precondition for making discoveries. My discovery about the instant color change involving the rotation of the elytra was worthy of a report in a scientific journal, so I wrote up my findings and submitted the article to Northeastern Naturalist, where it was reviewed by scientific colleagues and accepted for publication.
BURYING BEETLES ARE still common, as anyone can discover by putting out fresh meat. You don’t have to go looking for them; they will come to you. Nicrophorids are for the most part not endangered. Nevertheless, Nicrophorus americanus, the largest beetle of the group, averaging about three centimeters long but sometimes reaching four, is on the list of endangered species in the United States. It has disappeared from 90 percent of its former home range, which included at least thirty-five states, and is now found in only five. Unlike all the other sextons, most of whom are half as long, N. americanus is splashed with bright orange-red on the head, thorax, and antennae. Not enough is known about its biology to explain why it is so large, has so much orange-red, and is endangered while most other species are not. Nicrophorids have some peculiar specialties of habitat and food. One species, N. vespilloides, buries its carcasses only in peat moss; another, as mentioned earlier, buries snake eggs rather than mice or other small carcasses. One hypothesis is that N. americanus specialized on passenger pigeons and that now there are not enough carcasses of similar size regularly available over most of its range.
Sendoff for a Deer
It must be I want life to go on living.
—Robert Frost, “The Census-Taker”
I HAD BROUGHT ANOTHER ROAD-KILLED GRAY SQUIRREL with me to camp. The weather in Maine in mid-June 2011 was too cool for botflies to be active, so the squirrel carcass had no maggots. But it was not too cold to rot—I was pretty sure the squirrel smelled good and ripe. If it did, would a vulture find it? And what would it do with the smelly carcass? Would it swallow it whole, as a great horned owl probably would? To find out, I left the bloated squirrel in a clearing in the woods, then made myself comfortable on the couch next to the window in my cabin.
A raven flying over the forest saw the carcass first. It swerved to the clearing and then perched silently on the top of a pine tree. After surveying the area for a few minutes, it spread its wings and swooped down to the ground beside the squirrel, hopped up and down a few times, then pulled out the eyes and some fur. But it was unable to tear through the skin. Instead it entered the squirrel through the mouth and pulled out a little meat and the brains. Then it flew off. I ran outside, slit the carcass open, and again made myself comfortable on the couch, hoping to see the raven return.
With the rotting entrails exposed, there would be a strong odor plume. Sure enough, less than an hour later I saw a shadow pass over the ground; a large bird was flying overhead and circling the clearing—a turkey vulture. A minute later it swooped directly over the carcass and, after circling for another minute, landed on the lone apple tree next to the squirrel. There it constantly turned its head, seeming to look in all directions except at the squirrel. After a while it preened, then spread its wings out to the sun, held them stationary, and nonchalantly preened some more.
Watching the vulture through binoculars from inside the cabin, I thought it looked gorgeous. Not a speck of dirt was visible on it anywhere. Its long, ivory-colored bill glistened. The vulture was showing its heightened emotion by blushing; its naked head had turned cherry red from the blood shunted there. Its upper neck, though speckled with a few sparse black feathers, was soon bright purple. Below the almost-bare neck skin shone a thick, shiny, black-blue ruff, contrasting with the dull brown wing feathers.
After sixteen minutes of perching on the apple tree, the vulture started to shift its attention from the surroundings overtly to the squirrel. Hopping closer from branch to branch, the vulture finally dropped down to the ground next to the squirrel. It stood stock-still for several minutes before starting to take delicate, skimpy bites. It
pulled on entrails and flung them to the side, then resumed tearing and taking tiny bits of meat. After thirty-four minutes it flew off, leaving the intestines and the almost-clean bones and skin. I left them, wondering if something else might come along to take these leavings.
I woke at sunup the next morning to the sound of a crow, and as I looked up from my bed by a window I saw it perched on the tiptop of a tall spruce near the apple tree. The spruce was swaying in the breeze, and at times the twig on which the crow was standing bent over from the bird’s weight. But the crow kept its balance, cawing at the same time, for at least ten minutes. It was facing the squirrel remains, less than a hundred meters away, and I expected it to fly down at any minute. But it just kept up a vigorous cawing.
After a while a second crow chimed in from the valley below; when it arrived, the two flew to the apple tree where the vulture had perched the day before. Finally one of the pair flew down to the squirrel, landed near it, looked at it for about a minute, then flew back up into the apple tree. Both crows stayed in the nearby trees for a few more minutes and then, just as the sun was coming up, they flew off down the valley in silence.
An hour later a raven came flying in, and without a moment’s hesitation fluttered directly down to the squirrel carcass. It picked up the remains in its bill and flew off into the dense lower branches of the spruce. The raven was almost hidden there, but I saw it begin to pluck out fur. It quickly stopped and left the skin on a branch. That afternoon it returned, flying directly to where it had left the squirrel skin. There could not have been much left; when the raven flew off I found the skin, turned inside out (so the fur was inside), on the ground. A day later that too was gone. A larger carcass, I hoped, might bring even more of a crowd.
July of 2010 was hot and muggy in Maine. On the ninth, my friend Wallis, a builder in the village of Weld, near where I stay, and I were sweating as we put up the framework of a sauna. The heat, though oppressive for us, was ideal for deer flies. Ten to twenty were circling us at any given time, each one looking for an opening to press its attack—to make a cut in the skin to lap up fresh blood. I do not appreciate those who feed from me before I am dead, and every one of these flies intend to do just that. They scope you out by noisily zooming around you and then, in an unguarded moment, they land on any available bare spot of skin. A single deer fly doesn’t bother me, because I have learned their tactics and I know how to kill them. But with twenty at a time the odds are stacked in their favor.
These flies don’t bother just humans; they also drive the moose and deer in the woods to distraction. Moose may escape by submerging in pond water. Deer, which don’t browse on pond weed, have only the option of running and leaping. Apparently they don’t always look before they leap. That day, while Wallis and I were driving between Dixfield and Weld to get the cedar planking, we found a dead doe that had gotten smacked, and not too recently; it already smelled pretty ripe. I can’t imagine driving along, hitting a deer, and then leaving it by or on the road. And no one else had stopped either.
I did stop, as I often do, and I was sorry to find that the doe’s teats showed she had been lactating; somewhere nearby in the woods one or maybe two fawns would be waiting for milk and soon starving to death. It seemed a shame to let the deer carcass go to waste. With Wallis pushing and me pulling on a hind leg from the back of his pickup truck, we got her aboard and drove off. I wasn’t yet sure what to do with her, but I hoped that coyotes, bear, ravens, or vultures might find her in the clearing by my cabin. They would then feed their young and convert her into other lives, and in the short term they wouldn’t have to catch and kill something else.
I dropped the doe off among the goldenrod and meadowsweet bushes in my clearing. With my sharp hunting knife I opened her belly to spill the entrails, laying the scapula and right front leg over to the side. I also sliced the skin to expose the meat of a hind leg. Then, taking a break from building the sauna, I took up my post on the couch by the cabin window to see what would happen.
Two hours later the first turkey vulture came soaring in and started circling over the doe. A couple of times before I had seen swarms of vultures hunkering in the trees near a deer alongside the highway, perhaps waiting for traffic to stop. But my pair of ravens nest in the nearby pines, and they now had large, hungry young. This is going to be good, I thought. Here in the field, this could be a circus.
The previous fall my nephew Charlie, who lives in suburban Pennsburg, Pennsylvania, had claimed a road-killed deer in front of his house. He told me that “within an hour” after he gutted it there in his front yard, several turkey vultures arrived, and then more than a dozen gathered at the very fresh meat. They perched on the roof of his house for a short while and then, after apparently reaching some consensus, they descended together. By the next day not a scrap of meat was left. Only the stomach contents—partially digested corn the deer had harvested from neighboring fields—remained. I wondered how long it would take the vulture crew to arrive here at my deer, and if they would have to fight off the ravens or vice versa.
The vulture flew close over the carcass, rocking from side to side as these birds typically do. It then flew wider around the clearing and the nearby woods, as though checking everything out. But to my disappointment it apparently didn’t like what it saw, because it left without even landing.
From the work of the biologist Patricia Rabenold and from Charlie’s vulture experience, I knew that vultures have communal roosts, from which naive birds follow experienced ones to any communal feast. I expected a crowd of turkey vultures to arrive the next morning, so later in the afternoon I took the opportunity to do some errands. When I came back about two hours later, a vulture had arrived. It was perching on a tree at the edge of the clearing but flew off as soon as I came. It had not fed on the doe, though; nothing had been disturbed there.
The deer carcass was by now being discovered by hundreds if not thousands of blowflies. There are many blowfly species (1,100 have been described), and most require microscopic examination to differentiate, because in many cases you have to count the number of bristles to distinguish them. The common green blowfly, Lucilia sericata, has three bristles on the dorsal side of the mesothorax and six to eight bristles on its occiput (part of the head). Lucilia cuprina has only one occipital bristle. I didn’t count the blowflies’ bristles. I was already sufficiently impressed by the sheer brilliance of the green flies and their obvious difference from the blue ones, of whom there were fewer but whose metallic coloring was just as spectacular.
The carcass covered by these brilliant flies stank. I knew that a raven, as well as two vultures, had seen the carcass, because it circled the clearing once and called several times before flying on. Ravens like their meat fresh or, if not freshly killed, at least frozen. By dusk there were still no birds at the carcass, but after I went to bed that night I heard a coyote concert from the forest up toward Gammon Ridge. From upstairs I watched the clearing as the Big Dipper slowly rotated to the horizon. I strained to see gray shadows creep in toward the doe. But I saw none and soon slept well.
No ravens, crows, vultures, or coyotes came to the doe. But there was plenty of activity the next morning. Ten of my students from the winter ecology course I had taught at this site the previous January had come in the night and set up two tents in the field. Today was a designated party time, so ravens, vultures, and coyotes would stay away. I didn’t mind—here was a chance to find out what would happen to the doe when the big guys didn’t get to eat. The strictness of the big birds’ exclusion was assured by noon, when a second party of revelers arrived, bringing two bottles of elderberry wine and another guitar.
The gathering inside the camp that afternoon, and then outside around the campfire in the evening, was a fitting wake for a deer. Especially if she could appreciate the maudlin sounds of some ten voices chiming in and out to the accompaniment of two guitars, a banjo, and a mandolin. I might be envious, were it my turn to return to the cycle of life.
The doe reeked. I got whiffs of her even at the cabin. The chemical of putrefaction that is so offensive to us, ethanethiol (ethyl mercaptan), is, according to the Guinness Book of World Records, “the smelliest substance in existence.” For humans anyway. It is added in trace amounts to odorless propane so that we can detect it and not blow up our homes by lighting a match. Turkey vultures, supposedly attracted to even minute amounts of ethanethiol, have been used to detect the locations of leaking gas pipelines. However, the intensity of stink does not equal the degree of their attraction; turkey vultures come more readily to fresh or nearly fresh meat.
As I examined the doe on this second day, I saw that the blowflies had won the competition for her. The flies reputedly can smell a carcass from ten miles away, and they had indeed come in swarms, undeterred by putrefaction. The exposed meat was baking black in the sun, and the fur was covered with white patches—masses upon masses of blowfly eggs.