Note 62 — Chapter V
Reading edition
The best instances of sign-making among Invertebrata other than the Hymenoptera which I have met with is one that I have myself observed and already recorded in Mental Evolution in Animals (p. 343, note). The animal is the processional caterpillar. These larvæ migrate in the form of a long line, crawling Indian file, with the head of the one touching the tail of the next in the series. If one member of the series be removed, the next member in advance immediately stops and begins to wag its head in a peculiar manner from side to side. This serves as a signal for the next member also to stop and wag his head, and so on till all the members in front of the interruption are at a standstill, all wagging their heads. But as soon as the interval is closed up by the advance of the rear of the column, the front again begins to move forward, when the head-wagging ceases.