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Why are flies so hard to swat? Chalk it up to good planning

Aug. 28, 2008
Courtesy Cell Press
and World Science staff

Ev­er won­der how flies are so good at zip­ping off to avoid the swat­ter? A study us­ing fast, high-resolution vi­deo im­ag­ing of fruit flies has iden­ti­fied a key part of the an­swer, sci­en­tists say. Rath­er than just tak­ing off, the flies’ ti­ny brains first cal­cu­late where a threat is com­ing from, al­low­ing a care­ful prepara­t­ion for the es­cape.

Rath­er than just tak­ing off, fruit flies’ ti­ny brains first cal­cu­late where a threat is com­ing from, al­low­ing a care­ful prepara­t­ion for the es­cape, scientists say. (Im­age: NA­SA)


This be­hav­ior oc­curs about one tenth of a sec­ond ear­li­er than all pre­vi­ously iden­ti­fied com­po­nents of the es­cape re­sponse, the re­search­ers re­port in a pa­per pub­lished on­line Aug. 28 in the re­search jour­nal Cur­rent Bi­ol­o­gy

“We were sur­prised to find that ‘long’—in fly time—be­fore a fly takes off in re­sponse to a pred­a­tor or swat­ter it plans the di­rec­tion of the jump by mak­ing a rath­er com­plex se­ries of pos­tur­al move­ments,” said Mi­chael Dick­in­son of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy. 

Those move­ments care­fully po­si­tion the fly’s cen­ter of mass rel­a­tive to the legs so that leg ex­ten­sion pro­pels them away from the threat, he ex­plained. The cen­ter of mass is the spot where all of a body’s weight, on aver­age, is con­cen­trat­ed.

Those early move­ments aren’t re­flex­ively tied to flight initia­t­ion, the inv­est­i­ga­tors found, as a fly can ap­par­ently pre­pare for launch and then change its mind. “The fly some­how ‘knows’ wheth­er it needs to make large or small changes in its pos­ture to reach the cor­rect pre-flight stance,” Dick­in­son said. That feat sug­gests that the fly must in­te­grate vis­u­al in­forma­t­ion from its eyes with sen­so­ry in­forma­t­ion from its legs.

Dick­in­son em­pha­sized the im­por­tance of ad­vanc­es in high-speed im­ag­ing in the stu­dy. “These in­stru­ments have done for the time do­main what the elec­tron mi­cro­scope did for space,” he said. “As these in­stru­ments be­come more com­mon, I think we will see that an­i­mals per­form many be­hav­iors on rap­id time scales that simply evad­ed the de­tec­tion of our slug­gish eyes.”

He al­so hopes the find­ings in flies will give peo­ple a great­er ap­precia­t­ion for them, and make them “think be­fore they swat.”


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Ever wonder how flies are so good at zipping off to avoid the swatter? A study using high-resolution, fast video imaging has identified a key part of the answer, scientists say. Rather than just taking off, the flies’ tiny brains first calculate where a threat is coming from, allowing a careful preparation for the escape. This behavior occurs about one tenth of a second earlier than all previously identified components of the escape response, the researchers report in a paper published online Aug. 28th in the research journal Current Biology. “We were surprised to find that ‘long’—in fly time—before a fly takes off in response to a predator or swatter it plans the direction of the jump by making a rather complex series of postural movements,” said Michael Dickinson of the California Institute of Technology. Those movements carefully position the fly’s center of mass relative to the legs so that leg extension propels them away from the threat, he explained. The center of mass is the spot where all of a body’s weight is concentrated, on average. Those early movements aren’t reflexively tied to flight initiation, as a fly can prepare for launch and then decide against it, they found. “The fly somehow ‘knows’ whether it needs to make large or small changes in its posture to reach the correct pre-flight stance,” Dickinson said. That feat suggests that the fly must integrate visual information from its eyes with sensory information from its legs. Dickinson emphasized the importance of advances in high-speed imaging in the study. “These instruments have done for the time domain what the electron microscope did for space,” he said. “As these instruments become more common, I think we will see that animals perform many behaviors on rapid time scales that simply evaded the detection of our sluggish eyes.” He also hopes the findings in flies will give people a greater appreciation for them, and make them “think before they swat.” n