Mention foraging bees, and most people will picture insects flitting from flower to flower in search of nectar. But in the jungles of Central and South America, so-called vulture bees have developed a taste for flesh. Scientists have puzzled over why the stingless buzzers seem to prefer rotting carcasses to nectar. Now one group of researchers thinks it has cracked the riddle. The key came from looking into the bees’ guts.
“Bees are vegetarian,” notes Jessica Maccaro, “so these ones are a very large exception.” In fact, she’d go so far as to say these “are kind of the weirdos of the bee world.” Maccaro is a PhD student in insect biology. She works at the University of California, Riverside.
To study these bees, she worked with a team of scientists who travelled to the Central American nation of Costa Rica. In its jungles, vulture bees usually feed on dead lizards and snakes. But they’re not too picky. These bees will eat any dead animal. So the researchers bought some raw chicken at a grocery. After cutting it up, they suspended the flesh from branches in the trees. To deter ants, they smeared the string it dangled from with petroleum jelly.
“The funny thing is we’re all vegetarians,” says entomologist Quinn McFrederick, who also works at UC-Riverside. Entomologists are scientists who study insects. “It was kind of gross for us to cut up the chicken,” he recalls. And that gross factor intensified pretty quickly. In the warm, humid jungle, the chicken soon rotted, turning slimy and stinky.
But the bees took the bait within a day. As they stopped by to dine, the researchers trapped some 30 of them in glass vials. The scientists also captured another 30 or so of two other types of local bees. One type feeds just on flowers. Another type dines mostly on flowers but sometimes snacks on rotting meat. Central and South America are home to all three types of these stingless bees.
The bees were stored in alcohol. This immediately killed the insects but preserved their DNA. It also preserved the DNA of any microbes in their guts. This allowed the scientists to identify what types of bacteria they hosted.
Microbes live in the guts of animals, including people. Certain of those bacteria can help break down food. They also can protect animals from some toxin-producing bacteria which often live on rotting meat.
The guts of vulture bees had a lot more of a particular type of bacteria than did vegetarian bees. Those bacteria are similar to ones found in the intestines of vultures and hyenas. Like vulture bees, these animals, too, feed on rotting meat.
Maccaro and her teammates described their new findings November 23 in the journal mBio.
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Acid protection against rotten meals
Certain bacteria make the guts of vultures and hyenas very acidic. This is important because acid-producing bacteria kill toxin-producing bacteria in rotting meat. In fact, these microbes keep vultures and hyenas from getting sick. It probably does the same thing for the meat-eating bees, Maccaro and her team now conclude.
The meat-eating bees had between 30 and 35 percent more acid-producing bacteria than the strictly vegetarian bees. Some types of the acid-making microbes showed up only in the meat-eating bees.
Acid-producing bacteria also reside our intestines. The human gut doesn’t, however, have as many bacteria as do the guts in vultures, hyenas or meat-eating bees. That may explain why the bacteria on rotting meat can give people diarrhea or make us throw up.
Maccaro says it’s hard to know which evolved first — the gut bacteria or the bees’ ability to eat meat. But, she adds, it’s likely the bees turned to meat because there was so much competition for flowers as a food source.
The role of a meaty diet
David Roubik is the evolutionary ecologist who described how meat-eating bees find and devour their meals. He works for the Smithsonian Tropical Research Institute in Panama. Scientists knew the bees were collecting meat, he says. But for a long time, he adds, “nobody had the foggiest idea that the bees were actually consuming flesh.”
People had thought the bees somehow used it to make their nests.
He showed, however, that they were actually eating flesh, biting into it with their sharp mandibles. He described how once the bees find a dead animal, they deposit a trail of pheromones — signaling chemicals — on plants along their flight back to the nest. Their nest mates then use these chemical markers to track down the carcass.
“A large dead lizard placed 15 meters [about 50 feet] from one nest was located by bees within eight hours,” Roubik reported in a 1982 Science paper. It described some of his research in Panama. “Groups of 60 to 80 bees removed the skin,” he says. After then entering the body, they “reduced much of the carcass to a skeleton during the next 2 days.”
The bees consume some of the meat for themselves. They regurgitate the rest, storing it in their nest. There it will serve as a food source for developing bees.
The large numbers of acid-loving bacteria in the vulture bees’ guts end up in this stored food. “Otherwise, destructive bacteria would ruin the food and release enough toxins to kill the colony,” says Roubik.
Meat-eating bees also make surprisingly good honey by turning “partly digested dead animal material into sweet honey-like glucose,” observes Roubik. “I have tried the honey a number of times,” he says. “It is sweet and delicious.”