1988] Haskins & Haskins — Pheidole and Iridomyrmex 179 
Therefore, recourse was had to a different procedure. Ten specific 
sites were selected which has been censuses in the 1963 Haskins 
survey and in the surveys of Crowell and Lieberberg et al. and are 
still relatively unmodified physically, and a careful examination 
made of these. It was hoped that a survey of this kind would be 
adequate to answer at least the general questions posed above. In 
Table I the data for those sites are presented for the 1963, 1966, 
1973, and the current surveys. The data from Crowell were by neces- 
sity under-represented, because, unfortunately, the early Depart- 
ment of Agriculture surveys which he reports proved difficult to 
compare reliably with later ones, and because the maps in his publi- 
cation have been so reduced as to be difficult to interpret reliably, 
but the extensive accounts in his text are wholly consonant with the 
other material, and highly informative. 
Table II presents a summary of the shifts in distribution of P. 
megacephala and /. humilis at the ten selected sites as recorded by 
the surveys, proceeding from east to west in the Islands. 
Discussion and Conclusions 
The first conclusion from these data is clear and unequivocal: 
Thirty-three years after the first reporting of I. humilis in Bermuda, 
P. megacephala and /. humilis still coexist in strength there. 
Secondly, the earlier surveys have noted a consistent slowing in the 
rate of expansion of humilis as the territory has become saturated, 
and an increasing tendency for the patterns of distribution of both 
species to form an interdigitating, mosaic-like pattern, reminiscent 
of the patterns of mosaic distribution of three species of Lasius, two 
of Myrmica, and one of Formica described by Brian (1977) for a 
long-occupied British garden site. This tendency, together with the 
slowing expansion of both species, was noted particularly in the 
survey of Lieberberg et al. Both developments appeared to have 
progressed further in 1986. They may well suggest an approach to 
“saturation ” of the environment. 
The “equilibrium”, however, is clearly an uneasy and shifting one, 
with ground being continually lost and regained by both species: a 
feature also emphasized in the earlier surveys. It will be noted that, 
in the current tabulation of sites, only two, Spittall Pond Reserve 
and Ireland Island, have remained in consistent “possession” of one 
species ( P . megacephala) throughout the whole period. 
