“Then you put a coating of it around the tree trunks to keep off insects?”
“Certain moths whose caterpillars I fear came through my hedge. The girdle of tar put on at the base of the trunk is to prevent their climbing to the branches to lay their eggs. In that way I protect the fruit-trees from the caterpillars that a little later would destroy the foliage.”
“But moths can fly well enough, and your tar wouldn’t stop them. If they can’t reach the branches by climbing the trunk they will fly up to them.”
“For a moth that flies, agreed. If on the contrary it cannot fly, but has to content itself with walking, is it not true that the coating of tar encircling the foot of the tree trunk will prove an impassable obstacle? In the first place, the smell of tar is offensive to the moth, and then if it ventures on the sticky girdle it will infallibly become entangled and die, stuck fast in the tar.”
“That is plain,” assented Louis. “But are there any moths that can’t fly?”
“There are.”
“Are the lazy things afraid to use their wings?” asked Emile. “Perhaps they think it’s too much trouble.”
“How could they use them? They haven’t any to use, poor things.”
“That accounts for it, then. Moths without wings!”
“Yes, my boy, moths without wings. You shall [[376]]see some. This one is called by learned men phalæna geometra, which means geometer-moth You will soon see why it is so named.”