1984] 
Wheeler — Behavior of Procrypt ocerus 
179 
toire (Table 1 ) since it was produced only when ants were held and 
not under the standard conditions for observation. When an ant was 
provoked into stridulating, nearby nestmates did not obviously alter 
their behavior. The stridulatory file is located on the neck of the 
gaster where it inserts into the post-petiole. 
The presence and use of a stridulatory organ in Procryptocerus is 
remarkable as it is found in no other genus of cephalotines. The 
absence of a stridulatory organ in the Myrmicinae is unusual; Markl 
( 1973), in a survey of stridulatory structures in ants, found that 83% 
of myrmicine genera had them. So, it is intriguing first, that most 
cephalotines have lost the file and second, that Procryptocerus has 
retained the structure. Markl ( 1973) found the stridulatory organ in 
all 7 species of Procryptocerus he examined. 
Four subfamilies of ants have stridulatory organs: the Notho- 
myrmeciinae, the Pseudomyrmicinae, the Ponerinae and the Myr- 
micinae (Sharp, 1893; Haskins and Enzmann, 1938; Markl, 1973; 
Taylor, 1978). The stidulatory organ is always found on the same 
pair of segments: the file is located on abdominal segment IV and 
the scraper on segment III. In view of the apparent evolutionary 
stability of the stridulatory organ’s position, its presence in Procryp- 
tocerus can be regarded as a reliable primitive character. 
The ability to stridulate is common in ants, but the role of stridu- 
lation in communication has been demonstrated in only two cases. 
Markl ( 1965) showed that stridulation serves as a distress signal in 
Atta cephalotes. Buried workers stridulate and nestmates respond 
by digging in the vicinity of the sound. Markl and Holldobler ( 1978) 
have shown that in Novomessor, stridulatory signals function as a 
mechanism for modulating responses to other stimuli. For example, 
food retrieving behavior was enhanced when chemical recruitment 
stimuli were received concurrently with stridulatory signals. Novo- 
messor stridulates spontaneously, without the provocation of physi- 
cal restraint. 
Neither of these proven roles of stridulation applies directly to P. 
seahriuseulus. Digging is not an appropriate rescue response in an 
arboreal nest, and the fact that P. seahriuseulus does not stridulate 
spontaneously, without restraint, argues against an analogy with 
Novomessor. A third possibility is that stridulatory vibrations deter 
predators. This phenomenon has been documented in insects other 
than ants (see Masters, 1979). 
