1981] 
Carlin — Polymorphism in Orectognathus 
239 
combined, so that the polyethism curves indicated represent groups 
of tasks. There was a tendency to divide those tasks performed 
primarily by small workers among the size classes on the basis of 
size of objects handled and task location (fig. 3). Minors performed 
most in-nest maintenance; medias performed somewhat more out- 
of-nest maintenance than did minors. Minors contributed most to 
egg care. While both size classes attended larvae and pupae, minors 
contributed less to larva care than to egg care, still less to pupa care, 
medias compensating by putting more effort into care of larger 
brood. 
On the introduction of Solenopsis workers, the function of the 
guarding majors became apparent. As an alien ant approached, they 
spread their mandibles about 120° apart. When the tip of the 
invader’s head was within a major’s gape, the mandibles snapped 
shut, pinching the invader’s extremity with sufficient force to shoot 
it away like a squirted watermelon seed. This very effective defensive 
behavior, which was termed “bouncing”, kept nearly all alien ants 
from gaining entrance to the nest. Only majors, with their large 
mandibles and powerful adductor muscles, are equipped to do this 
properly (fig. 3). Major bouncers, guarding the tube mouth, could 
propel invaders backward for up to 8 or 9 cm; a single large media 
was able to bounce an invader, but not for very far. The blunt apical 
teeth of majors pinched but did not penetrate — invaders were not 
injured at all, just repelled. Ants of all castes struck at invaders that 
managed to get past the bouncers, majors contributing most to these 
attacks (fig. 3). They did not attempt to bounce a successful invader, 
but instead grabbed it in their mandibles and dragged it out, 
unharmed, after which they resumed the guarding position. 
Minor and media workers foraged in nearly equal numbers, but 
did not participate equally in predatory behavior. More prey was 
Figure 3: Polyethism curves of nest-centered activities, showing the percent 
contribution of workers of each caste to the total colony performance of given tasks. 
MI = Minor worker; ME = media; M A = Major. Some tasks are composites of several 
behavior categories in theethogram (table 1): Egg care = carry or manipulate egg + lick 
egg; larva care = carry or manipulate larva + lick larva + regurgitate with larva + feed 
larva solid food; pupa care = carry or manipulate pupa + lick pupa. In-tube nest 
maintenance = manipulate nest material + lick tube wall + remove refuse (in tube); 
out-of-tube maintenance = remove refuse (out of tube) + carry dead ant. Attacking 
alien ants and “bouncing” described in the text. 
