They are the ultimate scavengers.

Dermestid beetles - hard shelled, black, up to half an inch long - are among the most voracious creatures on earth. They are found almost everywhere in the world, and devour animal carcasses of all kinds. They will find one long before the vultures do and stay long after the big birds have gone.

And they are chomping away even now in dark rooms at major museums all over the world.

Ten years after man walked on the moon, museum osteologists use these creatures to clean the skeletons of animals to be exhibited to the public or catalogued away in collections.

"Your first reaction is 'how primitive,'" explained Laurie Wilkins, a dermestid expert. "But when you learn about them, you realize that it's a very sophisticated natural system. I guest nobody realized for years that they could be contained."

Wilkins used to take care of the dermestid colony at the Field Museum of Natural History in Chicago and is now establisng a colony at the Florida State Museum in Jacksonville. He remembers their drawing power on Members Night at the Field.

"They were the biggest hit in the museum," he said. "We had a crowd the whole time. 'Oh, how disgusting,' they would say, but then they couldn't take their eyes off of what was going on."

One can't watch them work without thinking of piranhas. They have sunk wooden ships and can chew through lead with ease. Their passion, though, is meat. They eat all the time. They have to. If they run out of food, they eat each other.

"It can turn into a regular Donner Pass situation," conceded Douglas John, who shepherds the dermestid colony at the Smithsonian's National Museum of Natural History. They are only carnivorous with their own species, he hastened to add.

"Sometimes I hear them in there," said Steve Medina. "It's like a humming sound. It means they're chomping away."

Medina, senior technician in the osteology laboratory at the American Museum of Natural History in New York, pointed to a room that is kept in perpetual darkness. A sign on its door reads "This door must not be opened."

Inside, in the stench and the humidity, thousands of dermestids consume small mammals, leaving their bones bare and intact, which is the way the museum wants them.

The process is not without its perils, though. Medina simply rolls his eyes at the idea of a mass dermestid escape from their black room.

"Forget about it, man, the damage they would do if they got out into the collection. They go for the hair, the soft stuff first, then the fatty meat and the tail," he said. "Just forget about it."

To avoid this nightmare, which is a worry to every museum that uses them, Medina brings in exterminators once a week to spray the rooms surrounding the beetle colony. As a backup, he keeps generous amounts of poison crystals in the animal skin in the museum collections.

Dermestids used to be te scourge of the fur trade and, according to John, bounties were offered to those who could rid hide warehouses of them. He tells the story, repeated by other dermestid cognoscenti , of a wooden sailing ship full of penguin carcasses which almost sank when it arrived in port in this country years ago because its hull had been riddled by dermestids during the voyage. Other ships, he had heard, had sunk under similar circumstances.

"Five of them wouldn't do much damage," Medina explained. "But put 2,000 of them together and you've got something going."

There is something charming about august institutions such as the Smithsonian and New York's Museum of Natural History, which have the most sophisticated tools availble, employing beetle labor. But it makes sense; the bugs take no salary, they work unblievable hours, they never strike, and they're always looking for more to do.

"They're very prolific, they're easy to keep, they're cheap, and they eat almost anything," explained Dr. Frank Greenwell, a museum specialist in the Division of Mammals at the Smithsonian.

Their only failing is that they work their grisly wonders only on smaller mammals. Anything above the size of a raccoon is boiled, bathed in chemical solutions or macerated, a tedious process in which bacteria slowly separate the meat from the bone while in water. There is no guarantee with any of these methods that the articulation, or structure of the skeleton, will remain intact. But articulation is not crucial with these animals, as their bones can be reassembled fairly easily.

With anything roughly up to the size of a raccoon, however, articulation is crucial for display as the bones are fragile, and until dermestids were first used in museum work in 1922, museum osteology technicians like Medina were doomed to extended bouts of time-consuming maceration. The state of the art took a giant leap forward with the introduction of the beetles who compare to the older methods as jet engines do to turboprops. Today, museums of any standing speak proudly of their dermestid colonies.

Medina, who as senior technician has maintained his relationship with dermestids at the Museum of Natural History osteology laboratory for 12 years, concedes that his job can be gruesome. Before he begins his work, one of the museum tanners strips the skin off of the favored animal. Medina then takes the remaining flesh and bones and "roughs out" as much meat as he can to save time. He's lucky if he gets half of it. Then it's off to the dermestids' room.

With larger animals, Medina says that the "roughing out" process can get awful. The stench of a large carcass, such as a gorilla from the Central Park Zoo during a summer heat wave, for example, is ghastly, and even with the aid of exhaust fans the work area reeks. As a result, Medina makes a point of completing such a job in one day. Smaller animals don't present the same problem, but the smells are still there.

The dermestids like it dark and humid, and that's what they get. Their room is windowless, and the humidity is kept high with the temperature at an even 80 degrees fahrenheit.

The beetles themselves are kept in six large, rectangular, wooden boxes in which they perform their various cleaning jobs. Beds of cotton are placed in each one for egg laying so they won't feel compelled to burrow into or through the wood. Medina likes to keep them working continually and will give them a new carcass as soon as they finish with an old one if he can. If not, he will give them some of the meat he has roughed out of other carcasses and refrigerated for just such a rainy day.

It is impossible to estimate how many beetles are in Medina's colony. He simply says "thousands." His colony is a good deal larger than the one in the Smithsonian, which lives in two such boxes. Because his crew is bigger, he can get the job done faster. "It's the ratio of bug mass to meat mass that is crucial," John explained.

The stench of the carcasses in the airless room is as strong as the scenes in the boxes are grisly when Medina turns on the light. In one box, the desmestids happened to be cleaning the remains of a snake, a large bird, and the head of a badger. They could have a human "squeaky clean" in about a week, Medina speculated, but noted they had never been used for this purpose.

He turned off the light and carefully locked the door. As he was leaving, he confided "I don't like the idea of being buried." CAPTION: Picture 1, Dermestid beetle larva, top; below dermestid larvae clean a frog carcass; photos by Donal F. Holway; Picture 2, no caption; Picture 3, Adult dermestid beetle; by Donal F. Holway for The Washington Post