1935] 
Beetles Associated with Ants 
223 
The small predaceous carabid, Tachyura incurva, on the 
other hand, is a year round occupant of the ulkei mounds, 
and is the most consistently abundant myrmecocole in the 
nest and trophoporic field. Schwarz (1889) thought the 
species an accidental visitor of ant nests, but later, with 
accumulation of data, reversed his opinion (1890). 
In the laboratory nests the food of incurva is highly 
diversified. The beetles feed upon dead or disabled individ- 
uals of their own species, dead and disabled host ants, the 
host brood, and dead insects brought into the nest by the 
worker ants. In addition, the ulkeicoles are also attacked 
where the species offers little resistance ( Leptinus testaceus, 
Atheta polita) , or are eaten when injured ( Microdon larvae, 
queens of the lestobiotic guest ant, Solenopsis molesta ) . 
Finally, incurva fed upon the sugar water and honey placed 
in the artificial nests. 
The nest conditions are apparently very favorable for 
the species and its general behavior has been discussed 
elsewhere (Park, 1929). It appears to be a tolerated 
form, or at least very successful in avoiding persecution 
by the host ants. Its catholic feeding habits fit it for the 
general role of nest scavenger, although it may be strictly 
predaceous upon occasion. 
We now turn to an habitual myrmecocole, the actively 
persecuted staphylinid, Megastilicus formicarius. It is com- 
mon in the nests of F. exsectoides (Schwarz, 1889; Blatch- 
ley, 1910; Wickham, 1900), and Wheeler (1926) discusses 
the relation of this latter host to the beetle upon (1) the 
red and black coloration and ant-like appearance of the 
species, (2) its defensive mechanism, which is similar to 
that of the related staphylinid Myrmedonia, consisting of 
emitting a volatile whitish fluid from the raised tip of the 
flexible abdomen, and (3) that the ants kill the beetle with- 
in a few hours when in laboratory nests, but are eluded 
easily by the beetles in nature. He found formicarius too 
feeble to kill living exsectoides workers. 
Formicarius has been taken repeatedly from the ulkei 
nests and studied in the laboratory. The above summary 
of its relations with exsectoides has been found to hold in 
general for ulkei. However, in the artificial nests of ulkei , 
formicarius is an agile and wary species. The ants attack 
