64 
Psyche 
[March 
be observed in either vial 4 or 5. This means that only concentrations 
of carbon dioxide which are harmless for these animals act as a 
highly efficient digging stimulus. No positive result could be reg- 
istered in the control experiment, which indicates that pure air is 
completely inactive as a releaser of digging behavior. 
If the C 0 2 produced by trapped workers of Solenopsis geminata 
is the only substance responsible for the release of the described be- 
havior, members of this species should also dig toward locked up ants 
of other species. I therefore trapped 150 workers of Solenopsis gemi- 
naia , 150 workers of the closely related fire ant Solenopsis saevissima 
(Myrmicinae) and 30 workers of Acanthomyops interjectus, belong- 
ing to a different subfamily (Formicinae) . The control-vial was 
empty. The 4 tubes were presented to the geminata- colony simul- 
taneously, and the results are shown in Table 3. 
All three species released digging behavior that is definitely above 
the control. The relatively small activity toward Acanthomyops in- 
terjectus is probably due to the fact that Acanthomyops species pro- 
duce volatiles which have a strong repellant effect against members 
of other ant species (Regnier and Wilson, 1968 and pers. commun.). 
Table 3. Results of the digging behavior of Solenopsis geminata 
released by trapped workers of Solenopsis geminata , Solenopsis saevis- 
sima and Acanthomyops interjectus. (Mean and range of ten repeti- 
tions) . 
Trapped species 
Average 
digging 
response 
Range 
S. geminata 
4.1 
1-6 
S. saevissima 
5.0 
O-IO 
A. interjectus 
2.8 
0-6 
Control 
O.I 
O-I 
Discussion 
C 0 2 is well known to attract the blood-feeding sexes of haemato- 
phagous arthropods (Reeves, Wiesinger, Carcia, Fallis and Smith, 
Nelson, Wilson et al., Kato et al., De Foliart and Morris, Thomp- 
son, in Anderson and Olkowski, 1968). Lacher (1964) found 
receptor cells on the antennae of workers and males of the honey 
bee which respond specifically to C 0 2 . Lacher (1964) and Boeck 
et al. ( 1965) speculated that this C 0 2 -response may serve the colony 
in controlling the concentration of carbon dioxide in the interior of 
the hive. Such a function, however, remains without proof. In the 
