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VII. On the Origin and Ancestral Form of Myrme- 

 cophilous Coleoptera. By H. St. J. Donisthorpe, 

 F.Z.S. 



[Read April 7th, 1909.] 



I AM working at a paper on how the eggs of Myrme- 

 cophilous Coleoptera get laid in new ants' nests, which I 

 hope to publish soon ; but it occurred to me that it might 

 be as well to publish first, as a preliminary paper, some 

 notes on how beetles first acquired the myrmecophilous 

 habit — that is to say, on the origin of the ancestral form of 

 ants' -nest beetles. Of course the ancestral form of any 

 species of truly Myrmecophilous Coleoptera is lost, and 

 unknown to-day, but it appears to me that by studying 

 the habits of those species which are occasionally and not 

 always found with ants, but more generally elsewhere, 

 we may learn how the ancestral forms of regularly myrme- 

 cophilous beetles first acquired their present habit of life. 

 When we speak of the ancestral form here, we do not 

 mean that of the present known ants' guests, but of the 

 Myrmecophilous habit itself, and the probable or possible 

 ancestral form of future generations of those species which 

 this paper embraces. 



* It is of course quite certain that the ants must have 

 been evolved long before their guests, and granted this, 

 then the guests themselves must have acquired their habit 

 by degrees, by developing and using the different means, 

 we see to-day in the regular guests, of defence against the 

 ants, and to please and be of use to them. If we study 

 the species about to be mentioned we shall see they 

 exhibit great variety both in the extent to which they are 

 found with ants, and also in their relations to their hosts. 

 Some have advanced much further along the road towards 

 being regular guests. Even in the true myrmecophilous 

 species, we can trace to-day evolution and development 

 at work — for example the forms or races of Dinarda in 

 relation to their different hosts (Zool., 1908, pp. 68-71), 

 the development of Hetaerius into a true guest from being 



* See " Some Notes on Myrmecophilous Spiders." Donisthorpe, 

 Zool., 1908, p. 420. 



TRANS. ENT. SOC. LOND. 1909. — PART III. (SEPT.) 



