PERSECUTED AND TOLERATED GUESTS. 



335 



distance straight to a F. cxsectoidcs mound and at once bury itself in 

 the earth and debris. According to Wasmann the larvae of the Ceto- 

 niine beetles are tolerated by the ants "partly with indifference and 

 partly with hostility." 



Among the most singular synoeketes are the larvae o^ the Syrphid 

 flies belonging to the genus Microdon. These larvae (Fig. 227), which 

 have been repeatedly described as mollusks (under the generic names 

 Scutelligera, Parmnla and Ceratoconcha \ or as Coccidse, are tough- 

 skinned, elliptical creatures, with a flat creeping-sole and a convex, 

 often prettily reticulated dorsal surface. They move about very slowly 

 in the superficial chambers of the nest. \Yhen ready to pupate, they 

 simply remain stationary 

 and attached to the walls 

 of the galleries by means 

 of their creeping-soles, as- 

 sume a deep brown color, 

 while the integument be- 

 comes indurated and more 

 brittle and forms the 

 puparium enclosing the 

 pupa proper. The fly 

 emerges by breaking off 

 the anterior dorsal third 

 of the puparium. Ver- 

 hoeff (1892) has observed 

 the fly in the act of ovi- 

 positing in the nest. It 

 was repeatedly, driven 

 away by the ants ( For- 

 mica sanyninca ), but kept 

 returning until the eggs 

 were deposited. Three 

 species of Microdon flies 

 have been bred from ant- 

 nests in Europe (M. muta- 

 bilis, dcrius and api- 

 fonnis ). Though the larvae of our American forms are not infrequent, 

 none had been bred until very recently, when Mr. William T. Davis and 

 myself ( 1908^ ) succeeded in raising specimens of J\l. tristis from a num- 

 ber of larvae found in Formica scJiaufussi nests in New Jersey and New 

 York. Another species is represented in my collection by some larvae 

 and pupae which I found in nests of F. obscuripcs, ciliata, etc., in Colo- 



26 



FIG. 228. Mimetic Staphylinids that live with 

 Doryline ants. (Wasmann.) A. Minieciton pu- 

 lex ; B. Ecitomorpha simulans ; C, Dorylostethus 

 wasmanni. 



