FINAL OBSERVATIONS ON PH El DOLE MEGACEPHALA 
AND IRIDOMY RM EX HUMILIS IN BERMUDA* 
By Caryl P. Haskins and Edna F. Haskins 
Haskins Laboratories, New Haven, Connecticut 
Introduction 
Pheidole megacephala (Myrmicinae) and Iridomyremex humilis 
(Dolichoderinae) are two well known invasive pest species of ants 
which, within approximately the last century and a half, have 
achieved almost worldwide distribution within the tropical to semi- 
tropical habitats available to them. Both are extremely aggressive 
and are capable of displacing native ant faunas on an impressive 
scale. Thus P. megacephala, originating probably in middle Africa, 
radiated extremely actively in both the Old and New Worlds as a 
“tramp” species, and by 1852, judging by Heer’s vivid account 
(Heer, 1856) it had thoroughly occupied, among many other west- 
ern European locations, the island of Madeira, exterminating a very 
large fraction (if not all) of the indigenous ant fauna. 
Iridomyrmex humilis, the “Argentine Ant” was first reported 
from Buenos Aires in 1866, and described by G. Mayr in 1868 
(Skaife, 1951, p. 7) (it may well have originally been indigenous to 
Brazil). By 1882 it had found its way (likewise as a “tramp” species 
exploiting human transport) to Madeira, which it occupied, in com- 
petition with the resident P. megacephala. It was a successful “occu- 
pation”, and by 1898, according to Stoll (1898) P. megacephala had 
completely disappeared from the Island, leaving /. humilis as the 
sole ant reported. Nothing is known of further details of the explo- 
sive interaction between these species in this limited island 
environment. 
P. megacephala reached Bermuda at least as early as 1902 (Dahl, 
1902), where it behaved essentially as in Madeira, displacing the 
greater part of the indigenous ant fauna and “blanketing” the 
Islands. By the time that one of the authors made a survey in 1927, 
its situation as a ubiquitous field and house ant closely resembled 
Heer’s account of it in Madeira seventy-five years earlier. 
* Manuscript received by the editor March 10, 1988. 
Ill 
