Death in a Meadow
(This 710th Buffalo Sunday News column was first published on November 7, 2004.)
The patrolling red-tailed hawk spots movement in the grass of an overgrown field. Its telescopic eyesight informs it that the slight motion is a feeding meadow mouse. The little vole has pulled down a ragweed seed head and is quietly chewing on it.
With this tasty rodent in its sights, the raptor plummets into the ragweed patch, its talons stretching downward toward the chestnut brown body. The light is wrong for this attack, however, and the big hawk's shadow warns the female mouse at the last minute. She dashes toward one of her cylindrical trails through the ground level thatch.
The distance between life and death is now, as it is so often in the wild, a matter of millimeters. The mouse almost avoids the hawk's clutches, but her hip is slashed by one of the outstretched talons. Although she escapes into the undergrowth under a patch of multiflora rose where the hawk cannot penetrate, she is now bleeding profusely and her brief life is draining away.
Anyone would describe that life as both precipitate and productive. She was born pink, hairless and blind just seven months earlier in a late winter brood, grew fur in a week and was weaned in two. She matured sexually when only a month old and mated over the summer with a series of males to produce eight litters of about a half dozen young each. Her grandchildren are feeding elsewhere in this same field.
By evening the little mouse lies dead but her story is far from finished. A steady rain reduces her scent so that two carnivores ‹ first a weasel and then a fox ‹ pass within a short distance of her body without finding it. Some distance away, however, the supersensitive antennae of a beetle pick up a few molecules of this reduced odor and he heads for the mouse. Arriving at the carcass his own excited pheromones draw a female to join him. These are burying beetles, gray, black and orange insects less than an inch long.
The two immediately set to work. They are remarkably strong, able to move the mouse's body away from the stones on which they find it through the tangled undergrowth to softer ground several feet away. There they remove the mouse's hair, clean and shape the body into a ball and deposit anal secretions on it to slow decomposition. At the same time they dig beneath the mouse to lower it several inches into the damp soil. This is not easy work and they are further delayed by almost constantly having to fight off flies and other competitors including burying beetles. But finally late on the third day the cadaver lies completely buried in an underground chamber.
The beetles work hard but they also find time to mate. Before the mouse is even underground the female oviposits two dozen eggs into the nearby soil. In just over four days those eggs hatch and are drawn to the chamber in which the mouse rests by its smell and cricket-like sounds made by their waiting parents.
Those parent beetles, who have already been gorging themselves on the carcass, now begin to feed partially digested mouse flesh to their young. The grubs rear up to beg for this food much as fledglings do in a bird nest. All but the bones, hair and bits of skin remain in about ten days. Soon after this the larvae pupate. They will emerge in a few weeks as adult beetles.
Even those remaining mouse parts do not go to waste, however. Soon after the burying beetles depart, other insects discover the remains. Checkered beetles feed on the bones, ham beetles eat the remaining flesh and clothes moths consume the hair. In other roles these same insects are known to homemakers as household pests.
Within weeks the mouse body disappears but all the atoms that made up this little rodent have now passed through the digestive systems of the carnivores that have fed on it to become part of the soil. Gilbert Waldbauer generalizes this process: "The garden soil that you crumble in your hand contains molecules that once composed the bodies of living animals, perhaps some from a mouse that burying beetles consumed only a few years ago, some from what was left of an elk after a pack of wolves devoured most of it a few hundred years ago, and even some from the body of a mammoth killed over 10,000 years ago by hunters of the Clovis culture."
The alternative ‹ the earth covered with dead bodies ‹ should make us appreciate Jean-Henri Fabre's assessment: "The sanitary officers of the fields are legion.-- Gerry Rising
Scott, Michelle Pellissier. 1996. Communal Breeding in Burying Beetles. American Scientist 84 (4):376(7).
-----. 1998. The Ecology and Behavior of Burying Beetles. Annual Review of Entomology 43:595-618.
Waldbauer, Gilbert. 2003. Recycling Dead Animals. In What Good are Bugs? Insects in the Web of Life. Cambridge, Massachusetts: Harvard University Press.