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Psyche 
[Vol. 91 
Discussion 
The metapleural glands have been considered characteristic of all 
ants with the very few exceptions given by Brown (1968). From a 
survey of external criteria Brown listed four categories where the 
metapleural gland appears to be atrophied: “1. Males of army ants, 
subfamily Dorylinae. 2. Males of a few other genera, mainly in 
subfamily Myrmicinae (e.g. Leptothorax duloticus, Tetramorium, 
Strongylognathus, Rhoptromvrmex, H Liberia striata ). 3. Workers 
of the specialized slave makers of genus Polvergus. 4. Queens of 
certain scattered ant species that are known (or assumed, on 
grounds of other morphological peculiarities) to be social parasites, 
i.e., those species which found their colonies in the nests of other ant 
species”. From these findings Brown developed an intriguing 
hypothesis about the function of the metapleural gland: “the gland 
produces a substance that, when tasted or smelled, says to another 
ant colony, especially one of the same species, ‘I am an enemy’.” 
According to Brown’s hypothesis “an individual either with the 
same odor-or-taste, or with none at all, would be treated by its host 
colony as neutral”. This would explain why certain species whose 
individuals have to enter a foreign colony (social parasites; doryline 
males) often do not possess a metapleural gland. 
This hypothesis was challenged by Maschwitz (Maschwitz et al 
1970, Maschwitz 1974). He was unable to experimentally demon- 
strate an enemy identification effect in the metapleural gland 
secretions, but he could show that in a number of ant species the 
metapleural gland secretions serve as powerful antiseptic substances 
that protect the body surface and nest against microorganisms. For 
example, the active antibiotic component of Atta sexdens was found 
to be phenylacetic acid, of which one ant stores an average of 1 .4 jug 
(Maschwitz et al 1970). In Crematogaster ( Phvsocrema ) difformis 
the secretions of the enlarged metapleural gland serve as antiseptics, 
but when discharged in larger quantities they can also repel animal 
enemies. Finally, in Crematogaster {Phvsocrema) inflata, which also 
possesses a hypertrophied metapleural gland, Maschwitz (1974) 
discovered that the sticky secretions function primarily as an alarm- 
defense substance. He hypothesized that in this case the antiseptic 
gland has evolved to become an alarm defense gland. 
Our discovery of the atrophy of the metapleural gland among 
more genera than previously suspected places this organ in a new 
