118 SIR JOHN LUBBOCK ON ANTS, BEES, AND WASPS. 
Observations on Ants, Bees, and Wasps. — Part XI. 
By Sir John Lubbock, Bart., M.P., D.C.L., LL.D., F.R.S. 
[Read 1st December, 1887.] 
On the Relation between Formica sanguinea and 
its Slaves. 
It is well known that Polyergus rufescens is entirely depend- 
ent on its slaves. Huber long ago found that this ant will 
starve in tbe midst of plenty, aud will not even put food into its 
own mouth. I have shown that isolated specimens will live for 
months if they are allowed a slave for an hour or so every two or 
three days to clean and feed them. It is said, on the contrary, 
that our only slave-making species, Formica sanguinea , can 
manage without slaves. Indeed, it appears that nests are 
sometimes found in which there are mistresses alone, entirely 
without slaves. Forel thinks that he has observed in such 
nests generally a larger proportion of small individuals than 
in nests which possess slaves. This would be interesting as 
tending to show that in such nests the young are less well 
nourished than when they have slaves to attend upon them. 
The question remains, of what advantage are the slaves to the 
F. sanguinea ? Forel says, I do not quite understand why, “ Je 
ne veux pas trop rechercher le motif qui pousse les sanguinea a 
se faire presque toujours des esclaves.” “ Peut-etre,” he adds, “ le 
sentiment de leur force, et le desir de travailler moins, pour faire 
plus a leur aise la chasse aux Lasius Jlavus et L. niger, est-il le 
mobile qui les pousse a cet acte. Celui-ci leur serait pen a peu 
devenu plus ou moins instinctif puisqu’il etait avantageux a 
la conservation de leur espece.” This suggestion seems very 
probable, and may be partially correct ; it is not, however, 
I think, a complete explanation. I have had under observation 
several nests of F. sanguinea. One of them I owe to the kind- 
ness of M. Forel himself, who sent it to me in June 1882. 
There was no queen, and, though the nest was very healthy, of 
course the numbers gradually diminished. At the beginning 
of January 1886 the last slave died, and there then remained 
only about 50 F. sanguinea. Under these circumstances the 
F. sanguinea began to die off rapidly ; by the middle of the year 
only six remained alive, and these, no doubt, would not have 
survived long. On July 1st I got some pupae of F.fusca and 
placed them outside the nest. The sanguineas soon discovered 
