The brains of flies are wired to avoid the swatter, US researchers said on Thursday.

At the mere¹ hint of a threat, the insects adjust their preflight stance to flee in the opposite direction, ensuring a clean getaway, they said in a finding that helps explain why flies so easily evade² swipes from their human foes³.

"These movements are made very rapidly, within about 200 milliseconds, but within that time the animal determines where the threat is coming from and activates⁴ an appropriate set of movements to position its legs and wings," Michael Dickinson of the California Institute of Technology said in a statement.

"This illustrates⁵ how rapidly the fly's brain can process sensory⁶ information into an appropriate motor response," said Dickinson, whose research appears in the journal Current Biology.

Dickinson's team studied this process in fruit flies using high-speed digital imaging equipment and a fancy fly swatter.

In response to a threat from the front, the fly moves its middle legs forward, leans back and raises its back legs for a backward takeoff. If the threat is from the side, the fly leans the other way before takeoff.

The findings offer new insight into the fly nervous system, and lends a few clues on how to outsmart a fly.

"It is best not to swat at the fly's starting position," Dickinson said. Instead, aim for the escape route.

Dickinson, a bioengineer, has devoted⁷ his life's work to the study of insect flight. He has built a tiny robotic fly called Robofly and a 3-D visual flight simulator called Fly-O-Vision.

苍蝇为何如此难打？美国研究人员于上周四称，这主要和苍蝇的大脑反应有关。

研究人员称，即使是很微小的危险信号，苍蝇在察觉后都能迅速调整好它的起飞姿势，然后向相反方向飞离，逃之夭夭。这一发现有助于解释为什么苍蝇如此难打。

加利福尼亚科技学院的迈克尔•迪金森在一份声明中说：“整个飞离过程十分迅速，只需约200毫秒。但就是在这么短的时间内，苍蝇就能确定威胁来自何方，然后启动一套动作，调整好腿和翅膀的姿势。”

迪金森说：“这就说明苍蝇的大脑能够非常迅速地将感官信息转化为相应的动作反应指令。”该研究报告在《当代生物学》期刊上发表。

迪金森的研究小组采用高速数码成像设备以及一个奇特的苍蝇拍对果蝇的逃命过程进行了研究。

当察觉到威胁来自前方，苍蝇就会向前微移中足，身体后倾，然后抬起后足向后飞离；如果威胁来自侧面，那么苍蝇则会将身体倾向另一侧，然后逃离。

这一发现让人类对苍蝇的神经系统有了更新的认识，而且帮助人们找到了打苍蝇的方法。

迪金森说：“打苍蝇时不能对准苍蝇。”正确的方法应该是对准它的飞离方向。

迪金森是一名生物工程学家，他一直从事昆虫飞行方面的研究。他研发了一款名叫Robofly的微型机器人苍蝇，以及一种名叫Fly-O-Vision的三维可视飞行模拟器。