Publ. 15. II. 1932. 
1 
Introduction. 
Among all the lepidopteral groups in the whole world the Geometridae may boast of the most universal 
and relatively most uniform distribution both in zoographical and topographical respects. We do not know 
any form of landscape which does not possess its specially adapted Geometrid forms and, excepting the polar 
regions where insects exist no more, there is hardly any country or island where we do not meet with some 
Geometridae. Even in those islands where cold-blooded animals are almost entirely lacking, such as Iceland, 
Fuegia, Tasmania etc., we still find a relative abundance in Geometridae , and, as we stated in the introduction 
to Vol. XVI, there are still whole colonies of Geometridae in those parts of the deserts where hardly any an¬ 
imals occur. 
Also in the vertical direction the Geometridae accompany us throughout the altitudes that can be 
reached by man and where insects can exist. Even above the tree-limit, in the close vicinity of the glaciers 
and snow-fields, we meet with peculiarly adapted Geometrid species or even genera, which are entirely depen¬ 
dent on these altitudes. On the one hand, there are genera or even species inhabiting a whole hemisphere in 
a scarcely varying form, and on the other hand there are large genera, the occurrence of which is confined 
to a single range of mountains. It is worth mentioning that alpine districts generally abound more in Geometrid 
species than the plains, which is probably due to the fact that most of the Geometridae prefer the forest 
which frecpiently covers the mountains. Especially the more imposing Geometrid species mostly emerge from 
tree-larvae, and that may be the reason why the larvae of Geometridae are of a relatively rarer occurrence in 
tropical districts than is the case in the temperate latitudes, where the access to the forests is not impeded. 
The total number of Geometrid species known at the time when the volume of the palaearctic Geo¬ 
metridae was being compiled (1914) had been estimated at about 10 000 (Rebel) divided between the various 
faunae as follows: about 1300 occurring both in the palaearctic and Ethiopian regions, about twice as many 
in the Indo-Australian region, and about four times as many in America. Meanwhile, however, the number 
of forms known has considerably increased, and just recently it has been growing enormously. Moreover, 
vast parts of our earth, particularly the alpine districts in Asia and America, have hardly been explored, so 
that our knowledge of this group is yet to be greatly augmented. In a very short time a great number of 
South-American towns will be fitted with electric light, which will simplify collecting. 
On the whole, the American Geometridae exhibit the very same consistency as those of the whole 
earth. All the Geometrid larvae, with hardly any exception, are provided with 10 feet, which peculiarity is 
solely confined to the larvae of this group. It is only the larva of a single South-American species which, when 
at rest, shows an attitude similar to that of the Geometrid larvae, clinging to the support with the claspers 
on the one hand, with the pectoral legs on the other hand, and freely stretching the body between the two 
supports like a dry twig; this, however, is effected by retracting the abdominal legs, the number of which is 
normal, until they disappear altogether, so that the resemblance to the attitude of repose is only apparent. 
The great consistency of the Geometrid larvae ist also exhibited by the pupae and even imagines. 
Nearly all of the pupae are slender, without any special distinction, resting almost unprotected or in a very 
scanty web which often consists of but few threads; or they lie in a kind of cradle, or simply underneath 
the mossy cover of the forest. The American Geometrid larvae have no real gregarious habits, nor do they 
gather in troups for the sake of pupation; if, as in North America, crowds of Geometrid larvae assemble in 
some district, this is mostly a consequence of cultivation which, for instance in the fruit-cultures of the United 
States, produces the occasional excessive propagation (e. g. of Alsophila pometaria) in the same way as the 
rapid growth of Bupalus piniarius is promoted by the fir-pine woods in Europe, or as the great devastations, 
VIII 1 
