290 BRITISH ANTS. 



workers must all know the way in order to be able to lead the 

 others. They must also possess the necessary memory to find the 

 exact spot again ; directions as to advancing, etc., appear to be 

 given by antennae strokes. The workers of sanguined only kill 

 individuals of the raided nests when they meet with considerable 

 hostile resistance, or when the defenders fasten on to their legs. 

 The main idea seems to be to terrify and frighten away their 

 opponents, and thus to obtain possession of as many pupae as 

 possible. Since the number of slaves present in a sanguined colony 

 is never as large as the number of cocoons captured during the 

 summer, it is evident that not all of the latter are allowed to hatch, 

 a number being used as food. Forel has seen a sanguined colony, 

 after pillaging one slave nest, proceed to another eight paces away 

 from the former and fifty from their own nest, robbing this also 

 before returning home 24 . 



Darwin attempted to explain the slave-making instinct in the 

 following much criticized passage : 



" By what steps the instinct of F. sanguined originated I will not 

 pretend to conjecture. But as ants which are not slave-makers 

 will, as I have seen, carry off the pupae of other species, if scattered 

 near their nests, it is possible that such pupae originally stored as 

 food might become developed ; and the foreign ants thus unin- 

 tentionally reared would then follow their proper instincts and do 

 what work they could. If their presence proved useful to the 

 species which had seized them if it were more advantageous to 

 this species to capture workers than to procreate them the habit 

 of collecting pupae, originally for food, might by natural selection 

 be strengthened and rendered permanent for the very different 

 purpose of raising slaves. When the instinct was once acquired, 

 if carried out to a much less extent even than in our British F. 

 sanguined, which, as we have seen, is less aided by its slaves than 

 the same species in Switzerland, natural selection might increase 

 and modify the instinct always supposing each modification to be 

 of use to the species until an ant was formed as abjectly dependent 

 on its slaves as is the Formicd rufescens." 3 * 



In spite of opinions to the contrary this is an accurate statement 

 of what does take place, for, as we have seen, other ants besides 

 the slave-makers do raid strange nests and steal the pupae for food 

 (Donisthorpea fuliginosd, Myrmicd, etc.), and will occasionally 

 actually bring them to maturity. F. sdnguinea has not lost the 

 instinct or power of working, both in the construction of their 

 nests and in bringing up and attending to their brood, and indeed 

 can live and prosper without slaves at all ; hence they have been 

 called facultative slave-holders. Wasmann has suggested that 

 fewer slaves are present in the largest and oldest colonies, and that 

 when a colony is old enough it ceases to make slave-raids 62 : but 

 this is not proved to be always the case. 



