IN 1869, the French astronomer, Leopold Trouvelot, then teaching at Harvard University in the USA, was conducting experiments on butterflies and gypsy moths he had brought from Europe. He was careless and one day a few gypsy moth caterpillars escaped from the cage in which he had kept them. He and his students searched for the caterpillars but could not find a single one. In the end, the astronomer called off the search, reasoning that a few caterpillars could do no harm.
But he was wrong. The caterpillars turned into moths, which in turn laid eggs and produced more moths. Gypsy moth larvae eat a variety of leaves and they are voracious eaters.