1941] 
Antiquity of Social Insects 
55 
different occasions among these insects. The oldest bees 
known are from the Baltic amber (Oligocene), and some of 
these belong to highly social families (Bombidse, Apidse). 
None of the described amber bees, however, can be placed 
in existing genera of these social families . 7 Furthermore, 
since none of the amber bees have been positively identified 
as workers, there is again no factual evidence that they were 
social. The social wasps (Vespidse) have a much weaker 
social organization than the termites or ants, and as in the 
case of the bees, social habits have arisen several times 
among the Vespidae and even within certain genera of the 
family ( e.g ., Steno g aster ) . The oldest known Vespidae are 
from the Eocene, and several Baltic amber species (appar- 
ently) belong to existing genera which include social 
species. This fact by itself does not, however, prove the 
existence of social habits among the Eocene or Oligocene 
wasps. Recent Vespidae have no structural characteristics 
definitely separating all social species from the solitary ones. 
Moreover, Recent social Vespidae scarcely ever show 
structural differences between the workers and the queen. 
As the geological record now stands, therefore, there is 
definite proof of the existence of social insects only as far 
back as the Eocene. Furthermore, only one Recent family, 
the Formicidae, has a social history extending into that 
period. The termites have probably had a well developed 
society for at least as long a time as the ants, though there is 
no paleontological evidence for that conclusion. The bees 
and wasps, also, may have had a social development extend- 
ing beyond the Eocene, but no fossil evidence for that has 
been found, and the nature of their present social structure 
is decidedly against that possibility. 
7 A true Bombus, B. proavitus Cock., has however been found in the 
Miocene of Washington (state). 
