Poison Perches

For two seasons a team of Cornell entomologists virtually lived with flies, doing their field work mostly in buzzing cowsheds. Like consumer-preference researchers, they tried to find what sort of perch flies like to settle upon. After long observation and many trials they decided that fin. strips of metal screening tacked to the ceiling are what flies like best.

Then the researchers dipped their screening strips in dieldrin, a powerful, non-evaporating fly poison, and tacked them up again. The flies took refuge on them in swarms--and died in five seconds. The poison remained effective for more than 16 weeks, slaying battalions of flies. The Cornell scientists believe that this anti-fly tactic is better than indiscriminate spraying of dairy barns and yards. The poison stays on the screening, never strays into the milk.

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