Abstract—Neurotic behaviour in one of a colony of large Black Ants (Formica fusca) was observed whilst demonstrating to a friend how an ant runs through an experimental maze. This ant had just completed an experimental run in the same maze and had only been back again with its comrades in the observation nest for a few minutes. When it was put into the maze for the second time it started to show twitching movements of its feelers and legs. It soon started off to run through the maze, which it normally did in about forty to fifty seconds without making a single mistake. Unfortunately on this occasion, when it got halfway through, it hesitated and made a mistake. Its limbs and feelers twitched spasmodically while it kept on trying to get through the wall of the cul‐de‐sac. These spasmodic jerkings got worse as the ant became more excited, and it soon started to circle backwards while still showing bad twitching movements, and eventually collapsed and became unconscious. This ant recovered when placed under a cold‐water tap for a few seconds.Since then I have observed several cases of comparable breakdown in ants and I have found a variety of ways of producing this sort of nervous breakdown in these insects.This paper describes these experiments and how they were linked with comparable experiments on some vertebrate