682 Ants’ Nests and their Inhabitants. [August, 
leaf-feeding species and the protected subterranean feeders would 
_ have produced either a modification of the sack or have caused 
its loss in the latter case, but there is no essential difference be- 
tween those living above and those living under ground, 
The odd-looking, spinous larva of Microdon, a dipterous spe- 
cies which has been twice described as a mollusk, is also found 
here only, while the flies themselves sport in the sunshine as do 
the others of their kind. A number of other Diptera larva are 
also found, many of them still undetermined. | 
Even the Lepidoptera have a representative here, and the larva 
of Helia americalis is found in the nests of Formica integra in 
great abundance. 
What purpose these larve serve in the economy of the nest, 
and what they feed on, isa mystery. Why the soft, fat coleop- 
_terous and dipterous larvæ are not devoured by the ants, is still 
to be discovered. The present theory is, that they feed upon the 
decaying or fermenting vegetable matter in the nest, and being 
thus useful as scavengers, are tolerated by their hosts. The 
mature insects seem to be of no use to the ants, and they make 
no effort to retain them. 
The third group, containing insects that are found in the ants’ 
nests in the perfect stage and nowhere else, is by far the most 
_ humerous. It comprises species of many orders and of widely 
_ divergent families, the Coleoptera being largely in the majority as 
= yet. A few of these true myrmecophilous species have been 
= found in all stages. Mr. Schwarz has found Euparia castanea m 
the nest of Solenopsis xyloni, a small ant not one-twentieth of 
the bulk of its guest, and making small hills only. The upper 
portion of the hilt is sometimes packed full of the beetles, and in 
_ the lower stories are found the larve. wes 
- Most of the species are known in the imago state only, and it 
_ has long been and is still a puzzle te entomologists where the 1m- 
_ Mature states of these insects are passed. They are truly my™ 
‘mecophilous, being found only in ants’ nests, and usually com 
fined to a particular species, 7. e., a species does not, except 1" 
rare instances, inhabit the nest of more than one species of ant 
n the other hand each species of ant has its own peculiar fauna _ 
of guests, so that it is possible with a series of guests at hand to 
l precisely from what ant’s nest they were obtained. : 
lese truly myrmecophilous species are again capable of sub- 
