“But it has wings, magnificent ones, all dotted with brown spots on a yellowish background.”
“Yes, and I will add that the forward ones have dark stripes. Now what do you think of this other moth?”
“That ugly thing isn’t a moth.”
“You judge by appearances, my dear child, and not by reality. This ungainly creature laboriously dragging along its big, naked, yellowish abdomen, with large black spots, is the female of the other moth.”
“I should never have guessed it.”
“Neither you nor a great many others. Henceforth you will know that there are numerous species of moths whose females are either wingless or equipped with such mere stumps of wings that they are unable to fly, whereas the males invariably have well-developed wings. Now, the male is not the one to be feared; it is the female with her eggs. The office of the tar girdle at the foot of the tree is to arrest the moth when it tries to climb to the branches where the laying takes place. Repulsed by the odor, it turns back; or if it persists in its endeavors to pass, it sticks to the tar and so perishes.”
“If the female laid her eggs somewhere else,” suggested Jules, “instead of on the branches—for [[377]]instance, on the ground—wouldn’t the caterpillars know enough to climb the trees by themselves?”
“The tar barrier would still be there to stop them. Besides, caterpillars hatched on the ground would hardly think of climbing the tree to the place where, in the usual order, the hatching would have taken place. As long as the customary conditions remain unaltered, insects show an astonishing instinct; beyond these conditions they do not know how to act.
“The caterpillar of the geometer-moth is gray with a yellow stripe running lengthwise on each side. It has a curious way of walking common to it and other caterpillars of the same group.
