Bees' Forearm Claws are Super Sensitive to Sweet Tastes, Study Finds

The claw-like mechanisms on honeybee's forelegs are highly sensitive to sugar and can be provoked to force the bees to extend their tongues, according to new research in the open-access journal Frontiers in Behavioral Neuroscience.

The sugar-detecting receptor - known as a sensilla - contains a bundle of nerve cells. In honeybees, these sugar sensilla are found in the mouth, on the antenna and on the tarsi, or end part of the legs.

The new research, led by researchers at the University of Toulouse in France, indicates that honeybees weigh information from each of their front tarsi to decide whether to feed.

For the study, researcher Gabriela de Brito Sanchez and Martin Giurfa, Director of the Research Centre on Animal Cognition at University of Toulouse, tested hundreds of honeybees.

Sugary, salty and bitter solutions were applied to the bees' foreleg tarsi to test of the bees extend or retract their tongue in the presence of a flavor. An extension of the tongue would indicate that the bee likes the taste and is prepared to drink the solution, the researchers said.

The study results revealed that honeybee tarsi - particularly at the claw end of the appendage - are highly sensitive to sugar, even in very diluted solutions. Additionally, the researchers learned that the bees' tarsomeres, the segments before the claws, were also highly sugar-sensitive.

"Honeybees rely on their color vision, memory and sense of smell and taste to find nectar and pollen in the ever-changing environment around the colony," Giurfa said in a statement. "The high sensitivity to salts of the tarsomeres and to sugar of the tarsal claws is impressive given that each tarsus has fewer sensilla than the other sense organs. The claw's sense of taste allows workers to detect nectar immediately when they land on flowers. Also, bees hovering over water ponds can promptly detect the presence of salts in water through the tarsomeres of their hanging legs."

A follow-up experiment presented the bees with contradictory information, such as one tarsi being swapped with sweet solution and another being treated with bitter.

"The central nervous system of honeybees weighs this information from both sides, but unequally," the researchers said. "Input from the side that is first to taste something tasty or distasteful counts for more."

If, for example, the bee tasted the sweet solution first, it was more likely to extend its tongue for a taste, seeming to ignore the unpleasant bitter taste.

If the order was reversed and the bee tasted the bitter compound first, it was about 50 percent less likely than normal to extend its tongue for sucrose, the researchers said.