CARBON DIOXIDE, A RELEASER FOR 
DIGGING BEHAVIOR IN SOLENOPSIS GEMINATA 
(HYMENOPTERA: FORMICIDAE)* 
By Walter Hangartner 
Biological Laboratories, Harvard University 
The behavior of ants digging through sand or clay in the direction 
of trapped nestmates has been described by Belt (1874) and Lafleur 
(1940). Wilson (1958) showed that in Pogonomyrmex badius 
(Latreille) this behavior pattern is released by a volatile substance 
originating from the mandibular glands. Later, McGurk et al. 
(1966) identified the responsible compound as 4-methyl-3-heptanone. 
At the same time, Blum and Warter (1966) isolated 2-heptanone 
from Conomyrma pyr arnica (Roger) and described its function as 
the releaser of alarm and digging behavior. Spangler (1968) re- 
ported that not only whole workers, but also amputated parts as well 
as larvae and pupae of Pogonomyrmex occidentalis (Cresson) attract 
workers of this species and release digging behavior. Forrest (1963) 
studied Lasius flavus nearcticus and four species of Acanthotnyops and 
found that workers also dig to free ants of another species but attack 
them as soon as they are released. 
During studies on a colony of Solenopsis geminata (Fabricius), 
I noticed that returning foragers started to remove a plug of cotton 
used to block the entrance of an artificial nest immediately after its 
mounting, even if the position of the entrance was rotated through 
180 0 . During most of these actions, they used their mandibles to 
chew away small pieces of the obstacle. The purpose of the present 
paper is to report on the finding that this behavior is released by the 
carbon dioxide produced by the ants trapped inside the nest. 
Material and Method 
During the whole experimental period, the same colony of Solenop- 
sis geminata was used. This colony consisted of several thousand 
workers, a queen, large piles of brood and a few hundreds of winged 
males and females which were all kept in a Wilson nest (Wilson, 
1962a). To examine the digging behavior toward trapped nestmates^ 
workers or other objects were trapped in the vial shown in Figure 1. 
A hole 6 mm in diameter was punched through the top of the plastic 
* Manuscript received by the editor March 16, 1969 
58 
