so many species to co-exist within very narrow limits, so that even three or four distinct kinds sometimes form their nests so close to each other that their galleries interlace and almost touch.
There are probably very few conditions of life (except those concerned with the nature and manner of obtaining food) which have a greater influence either in keeping creatures apart or in bringing them into collision, than those which constitute differences in their respective periods of activity and development. Thus, two species of which one has nocturnal and the other diurnal habits, or of which one is dormant while the other is active, may be said to travel different roads and to be complete strangers to one another. Complete separation of this kind is, of course, not the rule, and the greater number of species find themselves in more or less constant rivalry, but possess a sufficient number of points of dissimilarity in habit and requirements to make their co-existence possible.
It is curious to note what little differences, as they seem to us, may determine the fate of an ant. For example, the lizards will lie in wait for and greedily seize and devour the winged males and females of structor and barbara, though they dare not attack the assembled workers. It is curious to watch the way in which these worker ants will protect the winged ants which are about to leave the nest, by gathering round and swarming over them. When, as often happens, the nest is placed in an old terrace-wall, one may see the lizards creeping along or lying moulded into the inequalities of the stones, all having their eager eyes directed towards the swarm. One may then see the worker ants walk with impunity straight
