A new study reports that a mosquito’s sense of smell is more complicated than we once thought. And it may explain why this annoying insect is so good at seeking you out at a barbecue or in your bedroom and biting you — as well as lead to new strategies to prevent the potentially deadly diseases transmitted by its bite.

Meg Younger, a neuroscientist at Boston University, is co-author of the study. She exhales (呼气) gently into one of the mosquito-filled cages. A waft (股) of carbon dioxide blows across the insects, and they go wild. “And now, they’re looking for a target like the complex mixture of human body smell — a smell that’s attractive to the mosquitoes,” Younger explains.

In many parts of the world, this attraction isn’t merely an annoyance for humans. It’s a major health problem. Mosquitoes transmit diseases to humans. These diseases include dengue, Zika, chikungunya fever and malaria. The last disease alone causes over half a million deaths each year.

So scientists have attempted to break this attraction. But try as they might, the little mosquito has resisted. “They’re really good at what they do,” Younger says. Most of what we know about the neuroscience of smell comes from mice and fruit flies, where the wiring is fairly simple. Each neuron (神经元) in the nose has one kind of receptor (感受器) that detects a single kind of smell — say, a banana. And all the neurons with receptors for the banana smell connect to the same part of the brain. Younger and the others studied mosquito brains, where she found that each neuron has multiple receptors that can detect multiple smells.

This work could give researchers additional ways to battle the insects like developing traps that contain new smell mixtures that are more appealing than people.

“It’s an enormous study,” says Josefina del Marmol, a neurobiologist at the Harvard Medical School. She says there’s more work to be done to check, neuron by neuron, that each one actually responds to all the smells it has receptors for. But regarding the central finding, she says, “It really does change a lot about what we know of how insects perceive the world.”

Red squirrels are said to be smarter than other squirrels. They claim to fame --- and perhaps a sign of their intelligence--- involves maple trees. Red squirrels are known for harvesting sap in the late winter and turning it into a kind of maple syrup. Their maple sugaring technique is quite simple. In a study in the 1990s, scientists observed red squirrels making chisel-like grooves in the bark of a maple tree. After making the grooves in the tree, the squirrels left the tress! They returned to the tree about 24 hours later and licked up the sap that remained on the tree. By this time the water in the sap had evaporated leaving behind a high concentration of maple sugar.

Folklore even credits red squirrels with the origin of maple syrup. There is an Iroquois folktale that explains that Native Americans initially observed a red squirrel cutting into the tree bark with its teeth and later returning to lick the sap. An Iroquois youth observed this behavior and decided to use his knife to cut into the bark of a tree… thus discovering the maple tree’s sweet secret. A different legend relates the experience of an Algonquin chief. He struck a maple tree with his axe one day. His wife saw the tree wound dripping. She collected the sap in a wooden bucket and used it to boil the meat for supper. Both the chief and his wife were amazed at the sweetness of the meat that night.

Native Canadians and Native Americans showed the first settlers how to tap trees, harvest syrup and boil it. Maple syrup and sugar soon became an integral part of American colonial life. In 1685, a quote from the British Royal Society newspaper read: “ The savages of Canada, in the time that the sap rises, in the maple, make an incision in the tree, by which it runs out, and after they have evaporated eight pounds of liquor, there remains one pound that is sweet.” Soon maple sugar was the early colonists’ only sweetener, and this ended their dependence on foreign sugar.

Maple sugar is an excellent source of energy and flavoring, and even more important, it doesn’t spoil so that it is a source of food that lasts all year, until the next sugaring season. Today Canada makes more than 80% of the world’s maple products.