Before this study, researchers speculated that mosquito brains must have a complicated, sophisticated technique for distinguishing humans from other animals. Quite the opposite, it turned out.

"The simplicity surprised us," said McBride. "Despite the complexity of human odor, and the fact that it doesn't really have any kind of human-specific compounds in it, the mosquitoes have evolved a surprisingly simple mechanism for recognizing us."

— Read more in How mosquito brains encode human odor so they can seek us out at ScienceDaily.

When construction wraps up, Josefina del Mármol's new laboratory on the Harvard Medical School campus will look a lot like those that surround it, with rows of benches sporting chemicals, glassware, and computers.

What will set it apart are the scents: the citrus aroma of a compound called limonene; the clove-like fragrance of another compound, eugenol; the pungent odor of geosmin, reminiscent of a damp cave.

"It does smell quite unique because I use dozens of different odorants for my experiments," she said. "Some are pleasant, and some are awful, and the scent often lingers."

— Read more in Scent of a Human: Researcher probes mysteries of smell through disease-carrying insects at Harvard Medical School.

To dissect the observation, the team designed a new study that allowed hummingbirds to choose between a feeder with plain sugar water and an identical feeder containing sugar water laced with one of three chemicals: cuticular hydrocarbons found on honey bees’ exoskeletons; formic acid, a defense chemical released by Formica ants; and (Z)-9-hexadecenal, the ant aggregation pheromone they’d used in the bee study. The birds avoided feeders that smelled of the latter two, but not those that smelled of honey bees or a common food additive. “For specific contexts such as danger, they are responding to odors that are associated with . . . chemicals produced by insects,” says Wilson-Rankin. “They might not have many [olfactory] neurons, but they use those neurons to avoid dangerous [situations].”

— Ecologist Erin Wilson-Rankin studies olfaction in hummingbirds. Read more in Even the Tiniest of Birds Use Smell in Some Situations at The Scientist.