“Last autumn,” said Jules, “I found in the garden a large brown cocoon, and I hoped to see a beautiful butterfly come out of it; but this spring, to my great astonishment, out came a swarm of little flies.”
“What you took for flies was a brood of ichneumons. Yet there are flies, real flies, that lay their eggs in the bodies of caterpillars, just as the hymenopterous butterflies do with their terebra.”
“With their strange way of living on other creatures,” observed Louis, “ichneumons must destroy lots of caterpillars.”
“They destroy so many that often, if you take a hundred caterpillars haphazard from cabbages or other growing vegetables, you will find not more than two or three that are sound and in a condition to undergo metamorphosis.”
“Can those that have eggs in them be told from the rest?” asked Louis.
“Easily. The point pierced by the ichneumon’s terebra is surrounded by a little black spot. When you are gathering caterpillars it is well not to crush those that you see are pricked, nor yet those that [[357]]look diseased and have a loose skin. They are ichneumon-feeders, and their preservation means so many more swarms of ichneumons the next summer for the destruction of caterpillars.” [[358]]
CHAPTER XLIX
APPLE-EATERS
“Please tell us about the worm we find in apples and pears,” was Louis’s request one day when the children were gathered about their uncle.