Nature's curious
grave diggers


LORUS AND MARGERY MILNE WERE ON HOLIDAY in Ontario, Canada. Their summer cottage had been invaded by mice. Like most normal people, they decided to take defensive action. As one would expect, they had little trouble in trapping a number of the pesty rodents. But something unexpected happened when they discarded the little bodies by throwing them outside. They kept mysteriously vanishing overnight. So they tied a string to the dear departed mice in an attempt to discover what was going on. Each morning, to their surprise, they found the string neatly severed. Ingeniously, they decided to attach a fine wire tether to the murdered mice. Upon investigation the following morning, they found that the wire led underground, with the tethered mouse interred in a little burial chamber. Upon further inquiry, they discovered the funeral director's identity — a pair of beetles. These beetles show such caring behavior towards their young that many readers found it hard to believe when reading the earliest accounts written by Jean Henri Fabre.

This episode prompted a study of these minute animals which go by the appropriate common name of "burying beetles"; they are also known as "carrion beetles", or "sexton beetles". Worldwide, about one hundred species of these carcass-loving beetles belonging to the genus Nicrophorus exist. Some are widespread while others are found in restricted regions. Some have probably vanished; one giant kind that used to bury dead fish cast up on Atlantic beaches of the USA is all but extinct. Their penchant for burying their “prey” as quickly as possible makes great sense in light of the army of thieves that would happily snatch the food right out of their mouths — other beetles, flies, ants, and, in some parts of the world, mammals such as raccoons. In tropical areas of South East Asia, where carrion eating birds and mammals are scarce, these beetles play a vital role in keeping the forest healthy, as do other insects which dispose of larger carcasses.

God must have had a wonderful time dreaming up the bizarre behavior of these creatures. A great deal of thought must have been applied to the task of working out the engineering problems involved. After all, it's no mean feat for a beetle to inter a carcass much bigger than itself without the assistance of tools of any kind — no bulldozers or ditch diggers, just the ingeniously-designed anatomy and intricate behavior of the beetle itself.

Burying bee­tles are quick to find and start work on the corpse of a small animal or bird. Naturally, it is a toss-up as to whether it is a male or female that first arrives upon the scene. Whichev­er, the first bee­tle to arrive immediately sets to work. Sooner or later a mate of the same species also haps upon the scene. Without mak­ing any getting-to-know-you overtures, it too sets to work. The two labor together in a loose cooperation that advances the common effort; sometimes one will dig away at the nose while the other pushes from the opposite end. Though it has been observed over and over that either partner may snatch a half-hour nap at any time, or even vanish from the scene temporarily. Who knows why?

Life Nature Library, Tropical Asia

God has programmed some fascinating behavior into the living computer that comprises the burying beetle's brain. The beetle apparently finds the carcass by its fragrance. Invariably, it drops to the ground within three meters of the tender morsel, quickly folds its flying wings under its wing covers, then crashes through the ground litter to the carcass. Upon arriving, it assesses the situation. After only a moment of hesitation, it turns over onto its back, slides under the body, then lifts the mouse (or bird) slightly from the ground. Apparently it is testing whether or not the body is movable. It then emerges on the other side of its prey, rights itself, and begins testing the soil.

If it finds that the ground under the cadaver is too hard for digging, it will begin to explore at random for softer earth. If it finds such dirt no more than about three meters away, the insect decides it's worth the effort to move its treasure. And what a remarkable feat that is! It would be roughly the equivalent of a human moving an elephant's body! As one writer put it,

If there were a weight-lifting competition for insects, the burying beetle would be the champion, hands down. Or legs up: When these beetles push a dead mouse that weighs up to 300 times as much as they do to a suitable burying spot, “they're bench-pressing with six legs” while flat on their backs… (National Geographic, May 1992, Geographica).

The beetle alternates between hefting the body and taking a breather. Remember, God had to work out all the mathematics of this in detail. Does the beetle drag the corpse by the tail? No. That would probably prove impossible. Pushing it would also prove to be out of the question. To perform its herculean feat, the beetle first turns over onto its back, then squeezes its way under the carcass. It always proceeds under the end of the body nearest the burial site. Once in position, the beetle stays in the one spot and, by a series of leg presses, progressively inches the body forward, until the beetle emerges from under the opposite end. Every blade of grass is an obstacle, but the beetles somehow bend the blade or push aside a small piece of gravel with the moving body.

When finally the body is in the correct position, the beetles begin the daunting task of burial. They squeeze under the body, and commence bulldozing head­first into the earth. This loosens the soil. The loosened soil is then shoved out from under the mouse to the surface, and dozed over the top of it. Slowly but surely, a fraction of an inch at a time, the body disappears into the ground, until it is about an inch below the surface. They work at a fast pace, because they must bury their serendipitous find by dawn, or face the unwanted attentions of flies or ants.

The work doesn't end here. Once interred, the lit­tle gravediggers start working the mass of food into a compact ball. They free it of fur or feathers, perhaps adding secretions that modify the normal course of decomposition. As they clamber around the carcass, the walls and roof of the earthen tomb become firmly packed. The female constructs a short vertical extension of the chamber above the carrion, and lays her eggs there.

Two stages in the interment of a mouse by burying beetles (Milne & Milne 1976)

Man's poison is the beetle's meat. The very thought no doubt repulses the reader, but these beetles enjoy nothing so much as a sip of decomposing mouse juice. The female constantly works on the mouse (or bird) and, by a combination of selective feeding and clawing at the upper surface, prepares a conical depression in the carcass. Both beetles regurgitate into the depression droplets of partially-digested tissue. The fluid accumulates as a pabulum for the larvae that will soon hatch.

Observation of these beetles in specially de­signed glass-sided cages has revealed some amazing things. When the eggs have hatched, the larvae move to the conical de­pression, and dive wholeheartedly into the liquid contained therein. Funnily enough, the larvae do not just help them­selves to the nou­rishing fluid. It's the parent's responsibility to determine when the young are hungry. When meal time is decided upon, a strange thing hap­pens — the chil­dren are summoned to the meal table by means of a "dinner gong". One of the parents stands beside the pool and commences to stridulate. That is, it makes a cicada-type noise by rubbing built-in plectrums against equally built-in frets. The sound produced brings the hatchling larvae to the parent's side where they rear up instinctively like young birds. The parent then sips from the festering pool and transfers the fluid food of slightly degraded mouse or bird flesh to one larva after another. Yes, charming, I know. But hey, if you were a sexton beetle you would love it.

Mom tends her young (Milne & Milne)

By the time spring's warmth reaches the little subterranean cavern, the larvae have metamorphosed inside their pupal cases. They are now adults, ready to dig their way out and keep the wheel of life turning. Much more could be written about these wonderful examples of God's workmanship. Entomologists have been astounded by the ability of sexton beetles to solve the multiplicity of problems of logistics that they encounter in their daily activities. Even more, they have been amazed at their capacity to work out solutions to artificially-created problems that they simply would never encounter in nature.

God alone knows how and why.


Most of the information contained in this article comes from Milne, L. J., and Milne, M. August 1976, The Social Behavior of Burying Beetles, Scientific American Offprints, #1344

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