When it comes to quick and sometimes life-saving reactions, nothing beats the flies, as shown in a recent study conducted by biologists Gwyneth Card and Michael Dickinson from the California Institute of Technology and published in the August 28 issue of Current Biology.

The two researchers focused on the escape behavior of Drosophila, or the fruit fly. The experiments indicated that flies use visual information to plan a jump away from the looming threat. It appears that the flies begin to plan their escape 200 ms before takeoff, by making adjustments to their body position in the direction of their escape.

Furthermore, the two biologists explained that the flies position their center of mass so that leg extension will push them away from the expanding visual stimulus. What this goes to show is that flies are always on high alert and paying attention on visual information, which makes them capable of anticipating and avoiding dangers in a split of a second.

By using a high-speed video camera, the researchers studied the motion of fruit flies in response to a 14-cm-diameter black disk that fell towards the animals along a 50-degree downward trajectory. The result was that 96 percent of the flies jumped into the air and initiated flight once the black disk began its descending.

In order to determine whether flies bias their takeoff direction to avoid threatening stimulus, the researchers conducted further experiments, including changing the angle of approach for the black disk. The conclusion was that flies jumped backwards in response to looming objects in front of them, and forward in response to objects coming from behind them.

The flies appear to be using a combination of visual and mechanosensory cues to establish the direction of their escape. However, although mechanosensory cues might still have a role in their reaction to the incoming threat, flies mostly rely on visual information to make their escape.

The flies’ escape mechanism occurs 100 ms earlier than previously identified components of the escape response. The study also revealed that this behavior is not reflexively coupled to flight initiation, since a fly can prepare for an escape without taking off.

As for the early planning movement, the two researchers concluded that they must be triggered by an unidentified pathway that delivers visual information to thoracic circuits, which control leg motion. This mechanism appears to increase the effectiveness of escape by directing the fly away from the predator (however, that doesn’t mean that every escape attempt ends successfully).

The fruit flies may be hard to catch, but they did find their match in painted redstarts (Myioborus pictus), who appear to exploit Drosophila’s escape behavior. The tactic is to make the fruit flies go into the air, however, it still remains unclear whether the painted redstarts have a secret mechanism that anticipates the direction of the fruit flies’ takeoff.

“In structure, the fly’s escape behavior fulfills the criteria for motor planning, which is considered a hallmark of vertebrate cortex,” the researchers concluded. “Comparative neuroanatomical studies of insects suggest that such transformations may take place within the central complex, a set of evolutionary ancient midline neuropils in the arthropod brain. In the future, it will be of interest to dissect this behavior with the genetic and physiological approaches that are available in Drosophila.”