_Strongylognathus testaceus_ and _S. huberi_ live in association with _Tetramorium caespitum_, and are cared for by these latter ants; it is notable that as in the case of the slave-making _Polyergus rufescens_ the mandibles of the _Strongylognathus_ are cylindrical and pointed, and therefore unsuitable for industrial occupations. {163}_S. testaceus_ is a weak little ant, and lives in small numbers in the nests with _T. caespitum_, which it is said to greatly resemble in appearance. The proportions of the forms of the two species usually associated is peculiar, there being a great many workers of _T. caespitum_ both in the perfect and pupal states, and also all the sexes of the _Strongylognathus_, of which, however, only a few are workers. This would seem to suggest that _S. testaceus_ attacks and pillages the nests of _T. caespitum_ in order to carry off worker pupae, just as _Polyergus rufescens_ does. But the facts that _S. testaceus_ is a weaker Insect than the _Tetramorium_, and that only a few of its worker-caste are present in a community where there are many workers of the _Tetramorium_, seem to negative the view that the latter were captured by the former; and the mode in which the associated communities of these two species are started and kept up is still therefore in need of explanation. _Strongylognathus huberi_ is a much stronger Insect than its congener, _S. testaceus_, and Forel has witnessed its attack on _Tetramorium caespitum_. Here the raid is made in a similar manner to that of _Polyergus rufescens_ on _Formica_; the _Tetramorium_ is attacked, and its pupae carried off to the abode of the _Strongylognathus_ to serve in due time as its slaves. The mandibles of _S. huberi_, being similar in form to those of _Polyergus rufescens_ are used in a similar manner. Although _T. caespitum_ is common enough in South-East England, it is to be regretted that none of the guests or associates we have mentioned in connection with it occur in this country. It is a most variable species, and is distributed over a large part of the globe. Our British species of Myrmicides, about ten in number, all belong to the group Myrmicini; none of them are generally common except _Myrmica rubra_, which is a most abundant Insect, and forms numerous races that have been considered by some entomologists to be distinct species; the two most abundant of these races are _M. ruginodis_ and _M. scabrinodis_, which sometimes, at the time of the appearance of the winged individuals, form vast swarms. The tiny _Monomorium pharaonis_ is a species that has been introduced into Britain, but now occurs in houses in certain towns; it sometimes accumulates on provisions in such numbers as to be a serious nuisance. Seventeen thousand {164}individuals weigh 1 gramme, and it is probable that a nest may include millions of specimens.