54 Psyche [March 
constructs as many as 16 to 20 earthern cells, arranged in a 
crude comb. 5 
Since incorrect and misleading statements about the 
geological age of social insects are common in both en- 
tomological and paleontological literature, 6 we include here 
a summary of the evidence bearing on the subject. Parental 
care of young occurs in many groups of insects (e.g., 
Embiaria, Hemiptera, Dermaptera, etc.), but truly social 
habits among Recent insects are confined to members of two 
orders, Isoptera and Hymenoptera. The earliest Isoptera 
known are from the Eocene period and the group is well 
represented in the Baltic amber (Oligocene). Since only 
the winged or sexual forms have been found fossil, we have 
no factual knowledge that these Tertiary species were social. 
However, inasmuch as the social organization of the termites 
is more highly developed than that of any other insects, it 
was probably well advanced even in the early Tertiary. This 
conjecture is supported by the presence in the amber species 
of the transverse suture along which the wing breaks after 
the insects have swarmed. 
The Hymenoptera as a whole have been found as far back 
as the Jurassic, from which Siricoid and parasitic types have 
been described. Social habits have been independently de- 
veloped many times within the order, as Wheeler has pointed 
out, but none of the social families have been found in strata 
below the Eocene. The Formicidse (ants), which are the 
most highly social of the Hymenoptera, are represented in 
several Eocene beds. The presence of workers among these 
Eocene species is conclusive proof that the ants had a well- 
developed society by that period. This is not surprising, 
inasmuch as caste differentiation of the Baltic amber ants 
was as advanced as that of Recent Formicidse. The social 
history of the bees (Apoidea) has clearly been very different 
from that of the ants, for as shown by several Hymenop- 
terists, social habits have been developed on at least three 
5 Bischoff has figured a nest of this solitary bee (Biologie der 
Hymenopteren, 1927, p. 222, fig. 94.) 
6 For example, a recent edition of a standard text of historical 
geology states that termites and “social ants” occur in Jurassic strata. 
Actually, neither of these groups has been found in rocks older than the 
Eocene. 
