1964] 
Wilson and Taylor — Fossil Ant Colony 
99 
The Polymorphism and Inferred Biology 
of Oecophylla leakeyi 
There are good reasons to regard the Mfwangano Island material 
as a sample from a single colony, perhaps the contents of one nest 
preserved intact. In evidence is the fact that such a large number of 
specimens in all stages of development were recovered from a volume 
of roughly only one cubic foot of rock. Also, and equally important, 
many of the immature forms are beautifully preserved in clusters. A 
single group of newly hatched larvae are joined together in a typical 
“microlarval pile” (Plate io). These groupings could have been 
preserved only if the colony had been subjected to a minimum of dis- 
turbance prior to fossilization. 
When we measured the head widths of all of the adequately pre- 
served pupal workers (the measurable adult workers were too few for 
our purposes) the results were startling. As shown in Figures I and 
2 the size-frequency distribution is of essentially the same form as in 
the living species O. srnaragdina. This particular distribution includes 
the following two important features : the separate distributions of the 
minor and major worker castes are nearly but not completely non- 
overlapping, and the majors are more numerous than the minors. So 
far as is known, the Oecophylla type of distribution is peculiar to the 
genus among living ants (Wilson, 1953). The polymorphism in O. 
longinoda was shown independently by Weber (1949) and Ledoux 
(1950) to be correlated with a division of labor in which the majors 
do most of the foraging and nest defense and the minors serve more 
as nurses. The allometry of the living Oecophylla , involving a narrow- 
ing of the metathoracic constriction with increase in size (instead of 
the reverse), is also unusual if not unique among living ant species. 
The same kind of allometry is exhibited by O. leakeyi . Thus O. leakeyi 
possessed the same unusual and quite specialized features of worker 
polymorphism retained by the modern members of the genus. This 
first direct demonstration of the nature of polymorphism in an extinct 
ant species shows Oecophylla to be conservative not only in morphology 
but in basic social organization. 
But this is not the end of the story. Further findings indicate that the 
leakeyi nest was arboreal, just as in modern species. Numerous larvae, 
pupae, and adults are attached directly to well preserved leaf frag- 
Explanation of Plate 11 
Left: head of holotype major worker, O. leakeyi. Right: fossilized 
microlarval pile of 0. leakeyi. The maximum diameter of the larval pile is 
approximately 3.4 mm. 
