1962] Eisner and Happ — Infrabuccal Pocket 1 1 1 
EXPERIMENTS WITH GROUPS OF ANTS 
Within the formicine ant society, such evidence as we have suggests 
that regurgitative food transmission proceeds more or less continually 
— at least during that part of the year when the colony is active. 
Judging from the increased number of individual regurgitative 
exchanges that can be witnessed in laboratory colonies that are given 
renewed access to food following a period of deprivation, it is clear 
that the arrival of returning foragers with new crop-loads greatly stim- 
ulates the overall rate of intranidal exchange. Actual measurements 
made with species of Formica, fed on food labelled with radioactive 
tracer, have shown that the crop contents from single foragers may 
become shared by an entire colony in a matter of hours (Wilson and 
Eisner, 1957). Although no measurements have been made with 
Camponotus , it is unlikely that the results with this close relative of 
Formica would be much different. Evidently, an incoming crop-load, 
in the course of being passed from ant to ant, and channelled, as it 
were, through one infrabuccal chamber after another, could be expect- 
ed to undergo progressive filtration and ultimately be completely 
cleared of all debris. The following experiments proved that regurgi- 
tative feeding does in fact provide a means by which the communal 
crop supply is filtered and cleared. 
Seven ants, fed to repletion on a honey- iO/a corundum mixture, were 
each placed in a Petri dish with five unfed nestmates. A color marking 
differentiated the laden ant from the others. Regurgitative donations 
took place immediately, at the end of each of which the recipient 
(previously unfed) worker was removed and killed before it in turn 
had a chance to donate to others. Dissection of 25 recipients taken in 
this fashion showed 22 of them to have corundum in their infrabuccal 
pockets. Thirteen of these had their infrabuccal pockets packed full, 
and some particles had already passed into their crops. 
EXPLANATION OF PLATE 6 
Fig. 1. Intact worker of Camponotus americanus Mayr, shown next to two 
individuals whose appendages have been clipped, and whose gasters have 
been dissected away to expose the digestive tract. Only crop (A), proventri- 
culus (B), and midgut (C) are shown; the entire hindgut has been removed. 
Notice the enormously distended crop in the freshly-fed forager (center), 
contrasted with the crop of a starved individual (right). In Camponotus, as 
in many other ants, the crop acts as a social stomach, capable of storing 
amounts of nutrient far in excess of the demands of the individual forager. 
Fig. 2. Regurgitative food exchange between two workers of Camponotus 
pennsylvanicus (DeGeer). This is the process by which the liquid food 
supply in the crops of incoming foragers is shared with the remainder of 
the society. 
