1965] 
Scherba — Microtus 
I3i 
as a source of food as well as providing shelter for Microtus? 
A Microtus was live trapped and placed in an observation box 60 
cm. long by 30 cm. wide by 30 cm. high. A full shovel of nest con- 
tents and ants from the same nest as the Microtus was added tO' the 
box. 
Observations under these circumstances indicate that the worker 
ants did not avoid Microtus J but instead would attack it whenever 
the Microtus came into contact with the ants. When contacted by 
an ant, the Microtus responded by hopping quickly a few centimeters 
away. Ants which began biting a limb or the tail were usually quickly 
dislodged by flicking the leg or tail, or by cleaning the leg with the 
teeth. Some workers were not easily dislodged from the tip of the tail 
or nares. When bitten in these places, Microtus appeared to be “in 
j distress.” On another occasion, a newborn Microtus was seen 
writhing when attacked by opaciventris. 
It, therefore, seems evident that the ants do not avoid Microtus 
\ and that Microtus is not insensitive to, or completely protected against, 
ant bites. 
Content analysis of three stomachs examined under a dissecting 
microscope revealed only freshly chewed bright green plant parts. 
No recognizable insect fragments were found. 
DISCUSSION 
Clearly, Microtus exhibits few of the adaptations one might expect 
of a rodent which inhabits ant mounds. On this basis, we might 
speculate, as Professor Negus (personal communication) suggests, 
that for Microtus montanus ant mounds form a marginal micro- 
11 habitat utilized only after other, more suitable, sites are already 
\ occupied. In a year of apparent high Microtus density, this explana- 
j tion appears reasonable. 
We may categorize the relationship of this vole to the ant as that 
of a myrmecocole. (Park, 1929). 
ACKNOWLEDGEMENTS 
Mr. Norman Heryford, Smithsonian Institution, ably assisted this 
j work and his contribution is acknowledged with pleasure. Professor 
Norman Negus, Tulane University, kindly provided the determina- 
ij tion of the species of Microtus under discussion. 
Explanation of Plate 7 
Figure 1 — External openings of Microtus montanus tunnels at the base 
of Formica opaciventris mounds. A covering of vegetation has been removed. 
! Note forceps for scale. 
Figure 2 — Cross section of mound showing large central Microtus nest 
chamber. Dense, soft nesting material of plants has been removed. Note 
tunnel into chamber at rear. 
