No. 415.] NESTS OF AMERICAN ANTS. 529 
certain substances in the nests of their hosts, may be grouped 
together as clebtobiotic species. Owing to the present incom- 
pleteness of our knowledge, this category is not very clearly 
circumscribed, so that further researches may greatly extend 
its meaning or lead to its division into several categories. 
All the known cleptobiotic ants are of minute size and of 
subterranean habits. They are pale colored and seem to have 
a predilection for living with rather large ants. The minute 
species of Solenopsis (S. fugax Latr., orbula Emery, /atro 
Forel, molesta Say), and according to Forel ('94, pp. 23, 24) cer- 
tain species of Monomorium (M. andrei Saunders), and the 
species of the oriental genera Oligomyrmex, Melissotarsus, 
Carebara, Tranopelta, and Aéromyrma, belong to this cate- 
gory. Monomorium termitobium Forel enters into cleptobiotic 
relations with termites in Madagascar. Forel notes the fol- 
lowing significant facts concerning these different species : 
"It is more than probable that the extremely minute size and 
subterranean life of the worker of these species are the results 
of natural selection. The workers are very small, yellow, and 
blind, or nearly so, whereas the large females and males, of a 
brown or black color, with wings and large eyes, are witnesses 
to the fact that the minute size, etc., of the worker is due to an 
extraordinary regressive development. The female of Carcbara 
lignita West. is 20 mm. long and 4-6 mm. in diameter, while its 
Worker, which I owe to the kindness of M. Emery, is only 
2 mm. long! It is obvious that the minute size of the worker 
is its safeguard. For owing to its minuteness it succeeds in 
insinuating itself into the young brood of large ants or ter- 
mites without being seen by the defenders. It assassinates 
the young in their swaddling-clothes, incapable of defending 
themselves, As it lives very near its hosts, it requires neither 
size nor strength for seeking its food at a distance, and it is 
therefore in a position to nourish its enormous females and 
males with facility. Thus it is easy to see how this form of 
parasitism should lead to a diminution in the size of the 
worker, in depriving it of its eyes, and in giving it a pale color, 
while the females and males which mate in the air retain their 
Size, visual organs, and coloration.” 
