388 ANTS. 



nigrita black like the ants with which they live. These synoeketes are 

 also graduated in six.e according to their hosts, the largest and most 

 primitive form being dcntata (Fig. 224, B), whereas the others are 

 hardly more than >maller subspecies or varieties, which Wasmann con- 

 ceives to have been produced by a kind of unconscious selection on the 

 part of their respective host ants. D. dcntata is not uncommon in 

 sanguined nests, where it is usually tolerated with indifference. It 

 mingles freely with the ants, but when attacked, as sometimes happens, 

 it behaves like Mynncdonia and Megastilicus, raising the tip of its 

 abdomen and startling its pursuer. It feeds on dead ants and other 

 insects and is also fond of eating the ectoparasitic mites from the 

 bodies of the living ants and their other guests (Fig. 225). In this 

 capacity it is very useful to its hosts. When sangninca moves to a 

 new nest, it is accompanied by the Dinarda. This has been observed 

 by several writers, and during the summer of 1907 I myself saw near 

 Wiirzburg two of these beetles running along like ecitophiles in a pro- 

 cession of sanguinea workers that were carrying their slaves and pupse 

 to a new nest. 



To the symphiloid type may be assigned several of the guests of our 

 northern ants, but I shall here consider only the Histerid beetles of the 

 genera Triballns and Hetccrius and the Cetoniine beetles of the genus 

 Gremastocheilus. The numerous Histerida? that live with ants have 

 retained unmodified the hard, shining integument and seed-like form 

 of the free-living species, which constitute the greater bulk of this 

 family. Professor T. Kincaid has sent me a few specimens of Tri- 

 ballns californiciis which he took from nests of Mynnica inutica in 

 Washington. Though deep red, like many symphiles, this beetle has 

 no yellow trichomes and is therefore in all probability an indifferently 

 tolerated guest. The same is true of many species of other Histerid 

 genera (Myrmetes, Dendrophilus, Sternoca'lis, Erctinotes, Histcr,etc. ). 

 The genus Hctcerius, however, which is represented both in Europe and 

 North America, has the thorax and legs peculiarly modified and the 

 former sometimes furnished with trichomes. Forel (1874) and Was- 

 mann (1886) at first regarded the European H. fcrrngineits, when 

 living with Polyergus rufescens, as an indifferently tolerated guest 

 which feeds on the cadavers of the ants, but Escherich (1897), who 

 observed it in nests of Lasins alienns, is inclined to regard it as a true 

 symphile. The ants lick the beetle and carry it about, but have great 

 difficulty in seizing it with their mandibles on account of its hard, 

 smooth and rounded surfaces. Escherich describes one of their 

 attempts as follows : '' On uncovering the nest I saw an ant trying 

 to seize a Hetcerins. She persisted for a long time but her jaws kept 



