DIOPTIDAE. General Topics by Dr. A. Seitz. 
499 
5. Family: Dioptidae. 
This family containing about 500 lepidopteral forms has gone through many and continual changes 
with respect to its systematic insertion as well as to its composition. (For further particulars see p. 501.) Even 
to-day the synopsis, having been founded on the following statements, cannot be regarded as being final and 
unalterable. Packard who, though not felicitously, founded his systematic observations upon the pupae *), 
reminds us of the congruity of neurations between the Dioptid Phryganidia and Geometrid genera, such as 
Melanchroia, which, by the larvae, have been proved to be genuine Gecmetrae (Dewitz). The Dioptid pupa 
exhibits such a striking resemblance to that of Cleora that Packard is induced to insert the Dioptidae in his 
pedigree **) between the Cyllopodidae and the genuine Geometridae. The greatest confusion in trying to insert 
the Dioptidae was created by their wrong composition, since entirely heterogeneous elements were coupled 
together in quite an unnatural union. 
As may easily be gathered from the introductory words on p. 501, the mimicry chiefly caused this 
confusion, because even expert specialists confounded mimetic resemblance with phyletic resemblance. No¬ 
wadays we are fully aware in what complete way mimicry is able to conceal real relations and to put forth 
specious ones. This fact is particularly evidenced by the study of the living insect which, on being observed 
in its surroundings, by its behaviour reveals its true relationship to similarly coloured lepidopteral allies. The 
Dioptidae, as is stated below, are frequently diurnal insects, partly swarming in the sunshine ( Dioptis ), partly 
being very easy to rouse, and flying very skilfully and safely in the day-time ( Josia , Phaeochlaena), but sometimes 
also coming to the lantern in the night. The flight of the single species is entirely different and no less subject 
to the mimetic influence than the colouring of the insect is. The Dioptis areolata which does not copy any 
certain model, exhibits a whirling, swaying flight, like the unprotected day-fliers Orgyia antiqua or Drepana 
cultraria (and like nearly all the unprotected Heterocera flying in the sunshine have), which makes it extremely 
difficult to capture them with the net in the air, for instance a Bupalus piniarius or Lymantria dispar-rf ; in 
contrast with them, the Scea auriflamma , many Myonia and the variegated Getta exhibit the straight flight 
of their models, which are protected as P ericopinae or Arctianae by a very odoriferous oil ***) and have a rather 
rectilinear flight, such as the Arctiidae of all regions flying in the day-time, the Coscinia, Utetheisa, Rhyparia, 
Callimorpha etc., which partly fly onwards in an entirely straight line, partly only slightly flutter in their ilight. 
Those Dioptids, copying protected butterflies, fly exactly according to their models, as for instance Dioptis 
phaedima (70 c), which exactly copies the Danaid Hypoleria egla or aureliana (vol. V, pi. 41 a). In Josia ligula 
and ligata reproducing together with the Erycinid Mesenopsis the colouring of numerous Arctiidae the resenr 
blance in flying is so strikingly deceptive that, according to A. H. Fassl's statement, the Erycinid and Dioptid 
are not at all discernible when flying, and in settling down only by the Erycinid flying off more timidly than 
the Dioptid. 
The position of the Dioptidae has been rendered more intelligible by obtaining better — though still 
very scanty — knowledge about some of their larvae. The ventral feet on the middle segments have proved 
the independency of the group from the Geometrid tribe (which, however, is contested by Packard, who does 
not attach great weight to this fact *). Meanwhile, however, the larva of Phaeochlaena gyon has been made 
known by Mabilde, and has resulted in showing an unmistakable resemblance with the larvae of certain Noto- 
dontidae, as already the larva of Phryganidia californica by its bareness and its anal protuberance reminds us 
of the Notodontid genus Pheosia. 
The original appearance of the imagines of Dioptidae can the less be guessed nowadays as the uncommonly 
vast mimicry assimilating the species with the most heterogeneous models has scarcely left any traces of the 
original type. The principal groups from which the models are taken, are mentioned on p. 501, and it seems 
that their frequently very contrary colourings in some Dioptids have necessitated a rather incisive dyeing- 
*) Journ. New York Entomol. Soc. 1895, p. 30. 
**) American Naturalist 1895, p. 803. 
***) The scent of these models is somewhat like that of the Zygaena, thus similar to that produced by triturated or 
crushed Coccinetla. 
