10 
Psyche 
[Vol. 89 
As just noted, Cerapachys workers apparently sting each Phei- 
dole larva and pupa during the raid, before they transport the vic- 
tims to their nest. This appears to be a very stereotyped behavior. 
For example when 1 shook a Cerapachys colony which contained 
Pheidole larvae out of the nest tube into the arena, so that they had 
to move back into the nest, Cerapachys workers picking up a Phei- 
dole larva almost invariably went through the typical stinging 
motion pattern. They did not do this, however, when they picked up 
their own larvae. Although stinging behavior did not frequently 
occur inside the nest, occasionally I observed a Cerapachys stinging 
several larvae while reshuffling a pile. 
The Pheidole larvae are small and tender and the powerful Cera- 
pachys sting (Fig. 5) could easily pierce the larva and thereby kill it. 
Thus the injections of a paralyzing secretion through the sting has to 
be very subtle in order not to kill, but to preserve the larva. Brown 
(1975) describes the differentiated pygidium (Fig. 6) with its denticu- 
late margins, being present in all workers and queens of cera- 
pachyine ants. Brown states that “the function of the denticle- 
bordered pygidial plate is not known from direct observations, but 
it is assumed to have something to do with helping the insects to 
force their way through passages and cracks in soil or rotten wood, 
perhaps in connection with their entry into nests of termites or ant 
prey species”. 
Our morphological and histological investigations have revealed 
that these denticuliform and spinuliform setae on the pygidium of 
Cerapachys turneri and Sphinctomyrmex steinhei/i are sensory 
setae and comprise probably mechanoreceptors (Fig. 7). It is most 
likely that during the stinging process these mechanoreceptors sig- 
nal the gaster tip’s touch of the prey larva and the extent of the 
stings’ protrusion is thereby regulated. Many of the nonsocial acu- 
leate Hymenoptera, which paralyze prey by stinging, are equipped 
with mechanoreceptors on the tip of the sting sheath (Oeser 1961, 
Rathmayer 1962, 1978). We did not detect similar structures on the 
tip of the sting sheaths of Cerapachys or Sphinctomyrmex. In addi- 
tional experiments I further confirmed the suggestion that the prey 
larvae, captured by Cerapachys, are preserved alive. Approximately 
30 Pheidole larvae collected from a Pheidole colony were put with- 
out workers in a small test tube, which was kept moist by a wet 
cotton plug. A second similar test tube contained 30 Pheidole larvae 
which were taken from the Cerapachys nest. In two replications the 
