Publ. 13. IX. 1929. 
Introduction. 
Much more than any other faunistic region of the world, the Ethiopian fauna has influenced the 
facies of the Geometridae of this region. The conspicuous character of the scenery of Central Africa and of the 
Ethiopian parts of Arabia is the steppe alternating with deserts, which is verdant only during the wet season, 
whilst for the greatest part of the year it only bears dried stubble. The insect fauna exhibits rather few species, 
mostly also of a stunted habitus, so that the vast sandy plains appear to be dead during the greatest part 
of the year, and the animals of the steppes, which owing to the scarcity of vegetation have great difficulties 
in hiding from their rapacious persecutors, are forced to wear a sandy yellow protective colouring which we 
also find with a very great number of African Geometridae. In addition to this sand-colour, the African 
Geoyyietridae have the habit of settling on the bare ground with their wings spread out flat, a habit which is 
likewise exhibited by the few palaearctic (Teo?/^eb’^dae living on sandy downs (such sis Mesotype virgata, Tephrina 
murinaria and arenacearia and others). 
The Geometridae are more than the members of any other lepidopteral family able to feed on dry and 
withered plants, and they are therefore particularly well fitted to penetrate into the deserts. That is the reason 
why, in advancing through the Sahara we still encounter in remote oases whole colonies of Geometridae 
such as Rhodometra sacraria and the small Oar. The former species is numbered among the few lepidoptera for which 
the broad desert-zone of the Sahara does not form a geographical frontier and which may occur both in the 
northern parts of Africa and at the Cape of Good Hope. 
In the immense steppes of Africa, where trees are only of sj)oradic occurrence or altogether absent, we 
do not meet with any Geometridae the colouring of which is adapted to the bark of trees, a contrast to their great 
numbers in the palaearctic region. The Gnophos, Boarmia, Medasina, Elphos etc. which are entirely absent 
or sparsely represented in Africa, do not fit into the chiefly steppe-like landscape and can at any rate only 
propagate in the Hylaea and the countries with more hilly districts. Thus there are but very few groups of 
Geometridae that have been able to differentiate into a greater number of forms in the mostly monotonous African 
Continent, whereas the representatives of numerous other Geometrid genera that are widely distributed in all 
the other parts of the globe have not yet been discovered in Africa. Moreover, it is also probably due to the 
scarcity of trees or wood that the Pingasa, Terpna or Hypodoxa which are strongly represented in the Old 
World, are almost entirely absent in Africa proj^er, whilst in Madagascar, the fauna of wdiich is in many ways 
similar to the Indian fauna, they occur in few forms and but one species — Pingasa ruginaria (Vol. 12, pi. 5 d, f) 
— forming local races is distributed over the x 4 frican Continent. 
The general Geometrid type itself is presumably rather old considering the highly developed adaptation 
together with the almost entire absence of mimicry, the most equable distribution over the whole globe, and the 
rare consistency in the structure of the larvae, pupae, and imagines, beside the extremely complex variability in 
the colouring and marking of the different species. That may also be the reason why in the tropical regions 
— particularly those of Africa — Geometrid forms and individuals by no means occur in such great numbers 
as the phylogenetically young branches of the lepidopterous tribe; the Neotropidae, the Chalcosiinae, or Erycinidae. 
The same numerical superiority of Geometridae as occurs in Iceland, New Zealand, Patagonia, or Labrador, is 
also met with in the Cape Colony, at the borders of the Sahara, and in the Abyssinian high steppes, though 
not in the African Hylaea which otherwdse abounds so much in insects. 
As the members of the Geometrid family are rather feebly endowed with muscular force, they are more 
inclined to passive migration than to active migration. Only the members of a very limited number of Geometrid 
groups, such as Bupalus in the Old World and the Nelo and others from the Erateina-grou]) in the New World, 
are fit for continuous flights. Nearly all the species known hardly ever fly for great distances, and even the 
variegated day-fliers, such as Ematurga, Fidonia, Pardalodes, and Psetulo panther a, frequently rest during 
XVI 1 
