Oh to be a fly during the heat wave that blanketed the U.S. east coast this week. Heat sensors in the insects' antennae help them navigate temperature variations in their surroundings by guiding them away from heat. Turns out those sensors weren't all: Researchers have identified four large heat-monitoring brain cells (seen here in turquoise) that switch on whenever the heat rises above the fly's favored temperature, according to research published in Nature. Combined with a cold-avoidance mechanism in its antennae, the heat sensors help a fly stay comfortable until the sticky weather passes.