418 INTRODUCTION TO ZOOLOGY CHAP. 



difference between their own and their guests' offspring, the 

 ants unconsciously save themselves from being overrun and 

 exterminated by their treacherous pets. 



Slave- All the inmates so far mentioned have been 



making merely guests in the nest, but some ants keep 



Ants. other ants to work for them as slaves. One species 

 of ant in this country which shows a slight tendency towards 

 this reprehensible custom is the Red Horse Ant (Formica rufa), 

 which builds up over its nest the conical hillocks so common 

 in many pine woods, consisting of pine needles, dry leaves, 

 and twigs, rising sometimes to a height of 2 or 3 feet. 

 Living in these nests are often found a few of the small 

 common Ashy-Black or "Dusky" Ant (Formica fusca) helping 

 in the work of the nest. Their presence may be accounted 

 for in two ways. 



It is thought, though this has not been quite conclusively 

 established, that the queen of the Horse Ant after her 

 marriage flight often avoids the founding of a new colony 

 entirely unaided, by entering a small nest of Formica fusca, 

 and taking possession of it, killing the old queen, and inducing 

 the workers to look after the eggs which the invader now 

 proceeds to lay. In such cases the " rufa " colony would wax 

 numerous and strong, whilst gradually the " fusca " colony 

 would dwindle, until finally the conquered race might 

 disappear. 



It is also suggested by Lord Avebury that the Horse 

 Ant at times carries off the larvae and pupae of the " dusky 

 ant " for food, and that some of the pupae hatch out in their 

 nests, and remain with their captors. However, this is by no 

 means an established custom with this species of ant, as it is 

 with the allied Blood-red Ant (Formica sanguinea), which is 

 occasionally found in the south of England, making its nest in 

 a bank, though it is by no means common in this country, as 

 it is in other parts of Europe. This ant regularly makes raids 

 on the nest of the smaller "dusky ant" (Formica fusca), or of 

 another closely allied species, and carries off the brood, rearing 

 it and keeping the adults to help in the work of the nest. 

 These forays take place usually in the morning, the ants 

 marching in a rather straggling order direct to the nest to be 

 raided. They gradually surround it, and when all have 

 arrived they enter and carry off the larvae and pupae, only 



