16 THE CUCKOO BEES 



cuckoos are found as a rule to resemble 

 their hosts more closely, both in colour and 

 structure, and when we reach the social genus 

 Bombus (i.e. the humble bees) we find the cuck- 

 oos so like their hosts (pi. D, 30, 31) that even 

 entomologists of experience mistake one for 

 the other. Apis (the hive bee) has no cuckoo. 

 It seems to be theoretically probable that both 

 cuckoo and host once originated from common 

 parents ; this is suggested by the similarity 

 of structure of certain parts of both host 

 and cuckoo, even in cases where they are 

 otherwise most dissimilar. Andrena and Nomada, 

 for instance, which are very unlike, as stated 

 above, agree in both having very feeble stings 

 and in possessing three conspicuous spines on 

 the upper and posterior edge of the orbit of the 

 larva. Also, although Andrena the host has a 

 short tongue, and Nomada, its cuckoo, a long 

 one, the appendages (labial palpi) of the latter's 

 tongue are framed on the same plan as those of 

 the tongue of Andrena, and are quite unlike 

 those of the other long-tongued bees. On the 

 other hand, the cuckoos of the social species 

 resemble them so closely in structure as well as 



