DANAIDAE. By H. Fruhstorfer. 
191 
3. Family: Danaidae. 
By far the most of the species of this purely tropical family belong to the Indo-Australian Region 
and only a few reach the temperate districts of Asia. Three genera occur only in the Indo-Malayan sub¬ 
region, and only the genus Danaida has found its way also to Africa and America. The few non-Asiatic 
representatives of the genus Euploea, it is true, inhabit some East African outlying islands, which are 
perhaps remains of the old Lemurian bridge, but nowhere cross over onto the mainland. 
In contrast to all the other families of butterflies the Danaids are poor both in genera and species 
and their forms moreover show a very uniform stamp. They are only to a small extent subject to 
seasonal influences, especially compared with the Fierids, and a proportionately large number of species 
are distributed over large districts without varying locally. These conditions are only changed in those 
Danaids which inhabit the Archipelagos, where, though being still less inclined to form species than the 
Pierids, they nevertheless produce a series of sharply separated races, which in the last century were 
regarded as good species. Naturally the few inhabitants of the Oceanian islands have altered most; those 
on the islands lying off the continent less so, although occasionally on these the formation of species 
appears to have proceeded per saltum. Vulcan Island, which is scarcely 12 km. from New Guinea, al¬ 
ready produces a species which has not so far been found either on the main island of New Guinea or 
in its immediate neighbourhood. By far the largest proportion of the Danaids inhabit the plains; quite 
a number even do not ascend above the woods of the coast and in North Celebes I observed a Danaid 
flying high over the sea to the neighbouring islets. Only a few species inhabit exclusively alpine regions, 
and even these only quite exceptionally ascend above 2500 m. 
The Danaids probably belong to an old Rhopalocera-stirps, whose primitive pattern almost always 
follows the veins on the wings or shows remains of the ancestral stripes, and which is repeated in nearly 
all the other Nymphalid families and even in Pierids and Papilionids, on which account the Danaids are 
often regarded as models for convergent or mimetic species. 
Another indication of the great age of the Danaids is the filiform shape of the antennae, w'hich 
recall those of the ancestors or Lepidoptera (Protolepidoptera) and the primitive form of the genitalia, 
which are the most uniformly developed of all the known butterflies. On the other hand, the Danaid 
males are provided with the most complete secondary sexual organs, which rank among the most inter¬ 
esting physiological phenomena of the insect world. Besides the patches of modified scales along the inner 
veins of the hindwing many species possess also sack-like pouches, which are filled with androconia and 
onljr exist in the Danaids, and also moveable anal hair-pencils, which are looked upon as scent-organs. 
The hair-pencils of the Danaids consist of two parts, a tubular stylus and a rosette of radiating 
hairs of several mm. in length. The rosette oi hairs is as a rule concealed in the stylus. In some species 
a light pressure is sufficient to project it from the tube. In plexippus the flexibility of the anal pencil 
appears to depend on the time of year and perhaps also on the nature of the food which the butterfly is 
taking. 
The scent-organs of the Danaids consist of elongated sacs, surrounded by a flexible chitinous 
membrane, and placed on each side on the abdomen from the seventh to the middle of the fourth ab¬ 
dominal segment. Between them lies the muscular penis, which is surrounded by chitin. The scent- 
organs lie free in the body, only quite lightly fastened by fine muscles, and as they are not separated by 
any partition from the abdomen, they are probably directly nourished by the blood and projected by 
the pressure of the blood ;Illig). In my experience the colour of the fluid ejected by the anal pencil 
varies, apparently according to the food which the butterfly takes, for in some examples of the same 
species the stylus was green, in others again dark straw-colour. Danaids discharge a globular secretion 
through the anal scent-hairs, but Euploeids octahedral crystals, which in the basal part are of larger, 
distally of smaller size. The scent-patches appear as folds, whose opening is turned away from the vein. 
The interspace between the fold and vein is filled with live cells. 
Haase and others believe that the anal pencils play a part in copulation as organs of attraction. 
But according to my observations in Hong-Kong these organs, which look so delicate, seem rather to 
serve as weapons of defense or for frightening the enemy, for whether Euploeids were attacked by the 
wings or by the thorax, in every case they projected their anal pencil, moving it in the same way as 
wasps do their sting. The ejection of the hair-pencil is accompanied by the exhalation of a penetrating 
scent, smelling of honey. The scent-pencils of the Danaids are shorter than those of the Euploeids. 
Niceville once saw that Euploea core when flying about in the bright sunshine bent the ab¬ 
domen forwards to the thorax and in doing so projected the scent-pencils. 
