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Psyche 
[Vol. 91 
that the central location and general structure of the metapleural 
gland makes it ideally suited for distribution of an antiseptic 
secretion. 
Why then is the metapleural gland absent or strongly atrophied in 
Oecophylla, Polvrhachis, Dendromyrmex, most Camponotus, cer- 
tain social parasitic ants, and many male ants? Maschwitz et al 
(1970) offered the following explanations for the last two cases. 
Social parasitic ants, they argued, are usually highly attractive to the 
host ants, which groom them very frequently, so that the social 
parasites benefit from the social distribution of the antiseptic 
secretions of their host ants. This relieves the parasitic species of the 
burden of producing their own antiseptics and allows them to 
deploy the freed energy into other organs and functions. The 
absence of metapleural glands in male ants was given a different 
adaptive significance. Males live only a relatively short time inside 
the nest. They are also much less numerous than workers. 
Therefore, there exists no particular need for them to produce large 
amounts of antiseptic secretions. 
The latter hypothesis, of course, raises the question why in some 
species the males do have relatively large metapleural glands (Fig. 
7f, Tab. 1 ). The reason could be that in those cases the ratio of males 
to workers might be much higher and/or the males might reside 
inside the nest for longer periods and therefore would present a 
considerable “antiseptic burden” to the colony. This would favor the 
selection of males capable of producing their own antiseptic 
secretions. Furthermore, the metapleural gland of male ants could 
also have another, secondary function, which does not exclude the 
primary antiseptic function; that is, it could produce sex phero- 
mones and hence be an important character maintained by sexual 
selection. During mating females might thus favor males with well 
developed metapleural glands, and the capacity to produce larger 
quantities of pheromone. 
It is interesting that in all weaver ant species studied the 
metapleural gland was atrophied. The species we checked included 
Oecophylla, Polvrhachis ( Cvrtomyrma )? doddi, Dendromyrmex, 
Camponotus xenex. It is reasonable to speculate that these arboreal 
ants are much less exposed to microorganisms than terrestrial ant 
species, and therefore an antiseptic metapleural gland became 
unnecessary. 
