PSYCHE 
Vol. 92 
1985 
No. 4 
CRYPTIC PHRAGMOSIS: THE STRUCTURAL 
MODIFICATIONS 
By Diana E. Wheeler* and Bert Holldobler 
Museum of Comparative Zoology, 
Harvard University, 
Cambridge, Massachusetts 02138 
Introduction 
Cephalotini is an exclusively arboreal tribe of Neotropical ants 
that has specialized in passive defense. In the largest genus, Zacryp- 
tocerus, the entire body is heavily armoured and the expanded head 
surface of the soldier is particularly suited for blocking the nest 
entrance. Soldiers act as living doors, closing off nest entrances with 
their heads. Wheeler (1927) termed this phenomenon phragmosis. 
The most extremely modified heads within Zacryptocerus are found 
in the subgenus Cyathomyrmex, which is characterized by a com- 
pletely rimmed, saucer-shaped, cephalic disc on the heads of soldiers 
and queens (Kempf, 1958). 
Wheeler (1942) was the first to notice that in two species in this 
group queens and older soldiers tend to accumulate dirt on their 
heads. He also commented that the accumulation of this material 
made the heads resemble the bark of a plant and implied that the 
debris camouflaged this living gate to the nest. 
Recent discoveries of soil-binding pilosity in basicerotine and ste- 
gomyrmicine ants (Holldobler and Wilson, 1986) stimulated us to 
look for similar dirt collecting structures on these bizarre cephalo- 
tines. This led us to the discovery of remarkable features on the 
*Current address: Department of Biology, University of Southeastern Louisiana, 
Lafayette, Louisiana 70504. 
Manuscript received by the editor August 15, 1985 
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