8 TFIE DENIZENS OF AN OLD CHERRY TREE. 



Another parasite of P. lugnbris^ nine specimens of which 

 appeared in our boxes between April 27th and June ist, was a 

 brilliant member of the Golden Wasp tribe (ChrysididcB)^ viz., 

 Omalus auratus (Fig. 10, Plate II.), resembling, in splendour of 

 colours, the well-known ruby-tail fly {Chrysis igfiita), parasitic in 

 nests of mud-wasps {Odynerus), etc., but only about half the size 

 of that species. The ChrysididcE are, in every sense, Cuckoo flies, 

 for they make no nests, but lay their eggs in those of other Hymen- 

 optera, especially in those where provision has been stored for the 

 larvae. The little parasitic larva is hatched, and, it is said, feeds 

 in the larder with the larva of the original tenant, and when the 

 store of food is consumed it finishes up, not by ejecting its foster- 

 brother from the nest as the Cuckoo is said to do, but turns on its 

 companion, and sucks its juices. In the life-history of our Omalus 

 we had proof that this was the case, as, in each instance, we found 

 the pupal case of Omalus (Fig. 13, Plate II.) in the burrow of 

 Femphredon, and close to the remains of a larder, showing the 

 Aphides to have been eaten as well as the Pemphredon larva. 



In speaking of a species of Cuckoo-fly {Hedychrum) allied to 

 Omalus, a French naturalist said he observed it enter the dwelling 

 of a Sand-bee in order to lay its egg. The intruder was discovered 

 by the bee, who at once proceeded to turn out its enemy by laying 

 hold of her with its mandibles. But the Hedychrum rolled herself 

 up like a ball, and was invulnerable. The bee carried her out, 

 gave her a good shaking, bit her wings off, and left her. She, 

 however, had her way for all that, and crawled back again into the 

 nest, and laid her egg. From the structure of the tarsi and ser- 

 rated claws of Omalus (Fig. 11, Plate II.), we imagine our Cuckoo 

 fly quite equal to the task, even without wings, of returning to the 

 borings of Pemphredon^ after having been summarily ejected by 

 the enraged fossore. From the burrows of Pet?iphredon appeared 

 several species of Diptera, and taking them in the order of Mr. 

 Verrall's British list, we have first three species of the family 

 Myceiophilidce, or " Fungus gnats " of the genus Sciaria, the 

 imagines of which emerged from April to June, about forty speci- 

 mens being observed. The larvae of these species appear to feed 

 on the mouldy contents of the larders of the fossores, especially 

 where the store food had not, from some cause, been eaten by the 

 larva for whom it was intended. 



