348 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4TH Ser. 
islands are commonly barren but the higher ones intercept, in 
their upper portions, the moisture-laden atmosphere and thus 
not infrequently possess a luxuriant vegetation there. 
There yet remains a great deal to be done on the land in- 
vertebrates of the Galapagos and this is especially true of 
insects, whose habits and distribution are often specialized and 
restricted. The scanty list of bees and wasps shows a series 
of insects which have, I believe, reached their destination by 
the flotsam and jetsam method, and by flight. They certainly 
represent a very commonplace lot, easily adaptable to trans- 
portation to, and settlement in, such a territory. So far as I 
know the species, they do not show very much modification 
from mainland forms related to them. This is in sharp con- 
trast to the bees, wasps and other groups in general, of the 
more ancient and far more isolated Hawaiian Islands, for 
example. As in the Hawaiian group, insect immigrants are 
constantly arriving in the Galapagos. Beebe (Galapagos— 
Worlds End) noted the common milkweed butterfly (Danais 
plexippus) on Chatham Island in 1923 and this is the first 
record of that conspicuous and strong flying insect in the 
islands. 
The large carpenter bee (Xylocopa colona Lep.) and the 
Eumenid wasp (Pachodynerus galapagensis, n. sp.) are among 
just the sort of Hymenoptera one should expect in the Gala- 
pagos. One might well ask, however, why there are no social 
bees and wasps there when on the coastal mainland of Ecuador, 
600 miles away, they are among the most conspicuous and 
abundant of insects. Social insects such as these require a large 
amount of plant and insect food, a commodity not so abundant 
nor varied in the Archipelago; this, I believe, is an important 
reason for their absence there. 
