"If you follow an organism in the field for extended periods of time, and catalogue every type of activity for every moment of the day, you can't help but come to the conclusion, by George, this organism isn't doing much, is it?" said Dr. Joan Herbers, a zoologist at the University of Vermont, who has written comparative reports of laziness in animals. "Being lazy is almost universal." 

In fact, compared with other creatures, human beings spend anywhere from two to four times as many hours working, particularly if family, household and social duties are taken into account. 

But lest people feel smug about their diligence, evolutionary biologists are discovering that animal inactivity is almost never born of aimless indolence, but instead serves a broad variety of purposes. Some animals sit around to preserve precious calories, others to improve digestion of the calories they have consumed. Some do it to stay cool, others to keep warm. Predators and prey alike are best camouflaged when they are not fidgeting and fussing. Some creatures linger quietly in their territory to guard it, and others stay home to avoid being cannibalized by their neighbors. 

So while there may not be a specific gene for laziness, there is always a good excuse. 

"When you just see an animal that looks like it's in repose, you maybe looking at any number of very adaptive features," said Dr. Paul Sherman of Cornell University in Ithaca, NY. "You can't say it's simply doing nothing, and you can't always predict from common sense alone what the apparent rest is about." 

So diverse are the possible reasons for laziness that some biologists are beginning to shift the focus of their research. Rather than observing the behavior of animals in action, as field researchers historically have, they are attempting to understand the many factors that lie behind animal inertia. They hope that by learning when and why an animal chooses inactivity, they can better understand the key mysteries of ecology, like the distributionof different species in a particular environment and how animals survive harsh settings and lean times. 

"In the past, field biologists focused on movement, foraging, mating behavior," said Dr. Herbers. "Now they're worrying about why animals sit still." 

Animals certainly give their researchers much to fret over. Dr. Craig Packer and Dr. Anne Pusey, zoologists with the University of Minnesotain Minneapolis, have studies lions in the Serengeti since the 1970's, and they said that nearly all that time has been spent staring through binoculars at tawny heaps of fur, the pride's collective immobility broken only by the intermittent twitch of an ear. 

"A lion can lie in the same spot, without budging, for 12 hours at a stretch, said DR. Pusey. "they're active on their feet for maybe two or three hours a day." In that brief spate of effort, they are likely to be either hunting or devouring the booty of that hunt, which is one reason they need so much downtime. 

"A lion can eat an enormous amount in one sitting, maybe 70 pounds of meat," said Dr. Pusey. "Their bellies get extremely fat, and they look incredibly uncomfortable and incredibly immobile, lying on their backs and panting in the heat." 

Monkeys are commonly thought of as nature's indefatigable acrobats, but many species sit around as much as three-quarters of the day, not to mention the 12 hours of the night they usually spend sleeping. 

Dr. Franz de Waal, a primatologist at the Yerkes Regional Primate Center in Atlanta and author of "Peace-making Among Primates," said that he was amused to discover the lax habits of the woolly spider monkey, which he observed in Brazil with Dr. Karen Stryer. One morning the two researchers awoke before dawn to get out to a distant observation site by 7 a.m., when they assumed the monkeys would begin their day's foraging. 

"We were sitting there and sitting there," said Dr. de Waal. "By 11 a.m., the monkeys were still sleeping, at which point I fell asleep myself. 

Hummingbirds are the world's most vigorous and energy-intensive fliers - when they are flying. The bird turns out to spend 80 percent of their day perched motionless on a twig: at night, they sleep. 

Beavers are thought to bustle about so single mindedly that their name is often used as a synonym for work. But beavers emerge from the safe haven of their lodge to gather food or to patch up their dam for only five hours a day, give or take a few intermissions. "Even when they're supposed to be  most  active, they'll retreat back into the lodge for long periods of time, and rest," said Dr. Gerald E. Svendsen, a zoologist at Ohio University in Athens who studies beavers. 

The spade-foot toad of the south-western desert burrows three feet underground and refuses to budge for 11 months of the year. In that time, it does not eat, drink, or excrete waste, all the while conserving energy by turning down its core metabolism to one-fifth of what it is during its single active month. "If you find one of these dormant toads, you've got it," said Dr.Vaughn H. Shoemaker, a zoologist at the University of California at Riverside."it's just sitting in the soil like a rock or a potato." 

Even the busy bees and ants of Aesopian fame dedicate only about 20 per cent of the day to doing chores like gathering nectar or tidying up the nest. Otherwise, the insects stay still. "They seem to have run out of work to do," said Dr. Gene E. Robinson, an entomologist at the University of Illinois in Urbana-Champaign. "They really do look lazy." 

In his view, the myth of the tireless social insect probably arose from observations of entire hives or ant hills, which are little galaxies of ceaseless activity. "Human fascination with the industriousness of social insects probably comes from considering whole colonies rather than from considering what individuals in those colonies do," he said. "But since we've been tagging individuals to see what each bee does, we've found that any individual has a lot of surplus time. 

Biologists studying animals at rest turn to sophisticated mathematical models resembling those used by economists, which take into account ananimal's energy demands, fertility rate, the relative abundance and location of food and water, weather conditions and other factors. They do extensive cost-benefit analyses, asking questions like: How high is the cost of foraging compared to the potential calories that may be gained? 

Such a calculation involves not only a measure of how much more energy an animal burns as it rummages around relative to what it would spend resting, but also a consideration of, for example, how hot it will become in motion,and how much of its stored water will be needed to evaporate away heat to cool the body. Overheating can be a deadly threat for many animals. 

When they complete their computations, biologists usually end up respecting an animal's decision to lie low. 

For example, moose are ruminants, like cattle, and must stay fairly still while digesting food, he said. For every hour of grazing on vegetation, he said, the moose needs four hours to metabolize its food. "It has no other option but to be at rest." 

Researchers who have looked at hummingbird behavior have also concluded that the tiny birds are perfectly justified in taking frequent breaks. To hover in midair while sipping from long-tubed flowers, they must beat their wings in elaborate figure-eight patterns at a rate of 60 times per second. 

"The cost of their flight is among the greatest of any type of movement in the animal kingdom, said Dr. Frank B. Gill, curator of ornithology at the Academy of Natural Sciences in Philadelphia. "They burn more fuel in calories per dram of body weight when flying than anything else ever studied." 

Flying is so draining that many hummingbirds and their African relatives, the sunbirds, are better off staying motionless unless the food they can obtain is very rich indeed. To help assure that they can get nectar without having to travel too far for their dinner, sun birds will choose a territory and stand around on the perimeter, waiting for the flowers within it to become plump with nectar. 

For some creatures, immobility carries so many benefits that they become almost Buddha-like in their stillness. The fringe-toed lizard, which lives in the desert of the south west United States, sits motionless just below the surface of the sand for hours, with nothing sticking up but its eyes. As the lizards sit, the sand warms and invigorates them "They're ready to lurch out at anything edible that passes by, like a butterfly," said Dr. Philip Brownell, a biologist at Oregon State University in Corvallis. 

And should it see a predatory snake approaching, the lizard can further immobilize itself by suppressing its breathing. "The lizard just shuts off its engines," Dr. Brownell said. 

What is more, by staying snug in its sandy blanket, the lizard cuts down on water loss, a constant threat to desert creatures. 

In a harsh place like the desert, most animals spend most of the time waiting for water and coolness. Spade-foot toads come out only in July, when the annual rains bring insects to feed on. Male and female toads meet and mate the very first night they emerge from their rock-like state, and then they begin eating enough to put on an extra 30 percent in body fat to make it through their dormant 11 months. 

Several hundred species of mammals go into hibernation each winter, cutting down on energy expenditure by dramatically lowering their metabolic rates. In hibernating ground squirrels, for example, the heart rate slows to only one or two beats per minute, andthe body temperature goes down to near freezing. For herbivores, winter hibernation makes sense. "There's nothing for you to eat, the weather's bad, you can't reproduce, and there are still predators trying to eat you,"said Dr. Sherman. "The best thing to do is go into suspended animation." 

But sometimes a biologist is stumped over apparent indolence that cannot be explained by obvious things like inclement weather. Dr. Sherman has been studying the naked mole rat, a peculiar social mammal that spends its entire life underground. He long wondered why the largest mole rats in a group did the least and seemed to sleep the most, but he found out one day when he introduced a snake into the colony he had set up in his lab. 

"The big ones instantly sprang into action, and attacked the snake, "he said. "We'd thought they were sleeping, but they were just maintaining quiet vigilance." 

Such a need for vigilance may help explain why bees and ants spend so much time resting. Dr. Robinson recently has learned that honeybees have a soldier caste; members do little or nothing around the hive but are the first to act should the hive be disturbed. "They're like a standing army,"he said. "they're hanging around the colony, not doing anything in particular,but they can be immediately mobilized." 

Other bees and ants may be saving their energy for a big job, like the discovery of an abundant new source of food, which require overtime effort to harvest it, or the intermittent splitting of one hive into two, which suddenly leaves fewer workers to do the same tasks. "A colony has a labor force bigger than it really needs to get through those critical episodes," said Dr. Robinson. 

New studies show that social insects cannot afford to waste their energy on non-critical activities. It turns out that ants and bees are born with a set amount of energy to devote to their colony, which for reasons that remain mysterious seems to have less to do with the amount of food they eat than with an inborn genetic program. "They're like batteries," said DR. Peter Nonacs, who studies ants with Dr. Edward O. Wilson at Harvard University. "They have a fixed amount of energy in them, which they can use up quickly or slowly. The harder they work, the quicker they die."With that knowledge, Dr. Nonacs says he now has great sympathy when he comes upon an ant in repose. 

And perhaps biologists who study inactivity can even lend luster to the much-maligned creature that gave laziness its most evocative term: the sloth. Found in throughout Central and South America, the sloth hangs from trees by its long rubbery arms, sleeping 15 hours a day and moving so infrequently that two species of algae grow on its coat and between its claws. A newborn sloth sits atop its mother's belly and is so loathe to move that it freely defecates and urinates onto her fur; which she will only intermittently bother to clean. 

But lest such sluggishness seem almost perverse, the sloth is suited to its niche. By moving so slowly, it stays remarkably inconspicuous to predators. Even its fungal coat serves a camouflage purpose. With the algae glinting greenish-blue in the sunlight, the sloth resembles the hanging plant it has very nearly become.