The Moth & the Bomb

With the British passion for obscure enthusiasms, British entomologists have argued for years about the birthplace of the migratory moths that wing into Britain each spring. One theory is that they fly all the way from African deserts, where they maintain their winter breeding reservoirs. Another is that they breed somewhere along the way, so that only later generations ever reach England. In last week's Nature, Geneticist H.B.D. Kettlewell of Oxford offered strong proof for the direct-from-Africa theory--using an atom bomb explosion to trace the flight of the gentle moth.

Mindful that the French had set off an atomic blast in the Sahara a year ago, Dr. Kettlewell last spring collected early-arriving migratory moths and examined them under a Geiger counter. One specimen of Nomophila noctuella, a pale buff moth with a one-inch wingspread, showed a suspiciously high count. He pressed it on X-ray film and found that the radiation was coming not from the moth as a whole but from a single small spot in the thorax.

Next stop for the hot moth was Britain's Atomic Energy Research Establishment at Harwell. There, scientists found that its radioactivity was concentrated in a tiny, perfect sphere only 9 microns (four ten-thousandths of an inch) in diameter, just the sort of sphere that is formed by the billions when the fireball of a nuclear explosion touches and melts the surface of the earth. The sphere's age, measured by careful study of its radioactive decay, proved that it must be part of the fallout of the February test in the Sahara. Since the sphere was too big to hover in the air very long or drift very far, Dr. Kettlewell believes that his little moth acquired its radioactive particle before leaving Africa, carried it 1,500 miles to England.

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