Fabre conducted a famous study on the pine processionary caterpillar where a group of them followed head-to-tail in a circle around the rim of a flower pot; they continued marching in the circle for a week. He described the experiment in his 1916 book 'The Life of the Caterpillar". The study has been cited innumerable times by inspirational and religious speakers who view it as a metaphor for blindly following a leader or for confusing activity with accomplishment. Fabre considered his caterpillars to be mindless automatons, trapped because they were pre-programmed to blindly follow trails, in this case the endless one that they had laid down around the circular rim of the pot. More recent studies, however, indicate that the caterpillars were actually physically trapped on the narrow rim of the pot, their feet unable to gain the secure purchase that would be needed to descend its steep, vertical walls. In one experiment, groups of processionary caterpillars of the same age as those observed by Fabre were placed on a flat table top and surrounded be a circular glass ring, 8 inches in diameter and 1 inch high. The caterpillars soon moved to the edge of the arena where they began to circle, one behind another. They were allowed to procession in this manner until they had a well established trail along the edge of the ring. The ring was then removed, freeing the caterpillars of any constraint to their activity other than their trail. The circular processions persisted for an average of just two minutes before the caterpillars marched off in a straight line. However, when circular trails were established in a similar manner by younger caterpillars they continued to circle for as long as 12 hours after the physical constraint was removed, a considerable time but far short of the seven days observed by Fabre.