EARLY WARNING CUES FOR SOCIAL WASPS 
ATTACKED BY ARMY ANTS* 
By Ruth Chadab 
Biological Sciences Group, University of Connecticut 
Storrs, Connecticut 06268 
Colonies of social insects are well protected from most intruders 
by stings, bites, defensive chemicals, and nest architecture (Wilson 
1971, Jeanne 1975). Army ants of the Neotropical genus Eciton, 
however, prey heavily on a wide variety of ants (Formicidae) and 
social wasps (Vespidae:Polistinae) (Rettenmeyer 1963, Schneirla 
1971). Natural and staged raids observed on Barro Colorado Island, 
Panama Canal Zone, revealed how army ants break through defen¬ 
sive barriers of insect colonies. Surprisingly, though social wasps are 
often aggressive and larger than army-ant workers, most showed 
little or no attempt to defend their colonies and usually abandoned 
their nests after only brief contacts with the invading ants. Such 
rapidity of departure suggests 1) that the wasps use some mecha¬ 
nism other than direct contact with the raiding ants to detect the 
threat, and 2) that the wasps may “recognize” army ants with some 
specificity. To investigate these two possibilities the social wasp 
species Protopolybia exigua binominata (Schulz) was observed dur¬ 
ing raids and tested for its ability to detect army ants. 
Observations and Tests 
Protopolybia exigua is a small (length = 5mm) social wasp that 
makes a flat oval or hexagonal nest 4 to 12 cm long (Fig. 1). The 
single horizontal comb is attached to the underside of a leaf by 
several short petioles and is enclosed by a carton envelope having a 
small entrance near the edge of the upper nest surface. There may be 
30 to several hundred adult wasps in a colony. Nests are attached to 
a variety of plants, usually on leaves one to 4 m above the ground, at 
sites which are frequently explored by raiding army ants. Colonies 
of this wasp were observed to be raided by Eciton burchelli four 
times and by E. hamatum 10 times during two study periods totaling 
19 weeks on Barro Colorado Island. 
‘Manuscript received by the editor September 3, 1979 
115 
