March, 1901.1 57 



quietly ;iwj\y. Here, no doubt, one insect liad 8iui[)ly got into 

 another's hole by mistake: and again 1 have seen a Crabru uitcrruptus 

 ? go into the hole of an Osmia, but come out immediately, although 

 the owner was not at home. The mere fact, then, of an insect being 

 seen to issue from the hole of another does not necessarily prove any 

 biological connection between the two. But if the phenouienon occurs 

 repeatedly it will (in Dogberry's phrase) "go hard to be thought" that 

 there is such a connection. And I can say positively that in the case 

 1 have described above, the phenomenon occurred not once or twice, 

 but repeatedly throughout the whole period of observation. 



What the object of these constant visits of the SpJiecodes to the 

 Andrena burrows was, is another question. I saw them enter the 

 burrows, but I did not see them, and could not have seen them — even 

 if they did so — enter the actual cells far below the surface of the 

 ground in which the Andrena store their pollen and lay their eggs. 

 I suppose it is conceivable that they may have made cells of their 

 own among but apart from those of the Andrena, as certain small 

 ants are said to tunnel on their own account between the chambers 

 occupied by a larcer species, or as rats and mice make their own 

 houses in the walls of ours. But I see no reason for preferring this 

 or any other hypothesis to the more simple one— that they are 

 ordinary inquiliues ovipositing in the cells of their hosts and taking 

 advantage of the stores accumulated there. Some day, perhaps, the 

 ''X rays" will enable us to watch their actual proceedings after 

 entering an Andrena burrow, but till then it is to be feared we shall 

 have to rest content with hypotheses which may or may not be true. 

 And I must say that the hypothesis which seems best to explain all 

 that I have read or seen of the habits of Spliecodes, is that of its 

 parasitism, usually on Ilalichis, but sometimes also on Andrena. 



\ 



Since writing the above I have become acquainted with two 

 remarkable papers by M. Ferton on the parasitism of Spliecodes (Bull. 

 Soc. Ent. Fr., 1898, Eev. Scient., 1890). According to his observations 

 the parasite not merely infests the burrows of Halictus, but engages 

 in deadly battles with certain females of the latter, who are postea 

 (he says) as sentinels to defend not their own cells only, but those of 

 the entire colony (!), against the attacks of these marauders. Such 

 an organization for common defence implies, as he points out, that 

 Halictus is not only an industrious, but to some extent a social genus 

 — contradicting, it need hardly be said, the opinions hitherto generally 

 held on the subject. 



