86 Treubia Vol. Ill, 1. 



and 20 °/o wingless ones, of which number half have certainly come to the 

 island by ocean currents, against 81 o/^, igo/^ and lO^/^ in 1920—1921. 

 The difference is too slight to draw any conclusion for or against our 

 presumption. In this respect, also, it is most regrettable that investigations 

 into Krakatau's fauna have not been made right from the start. 



De Meyere, however, in his paper on the Diptera from Krakatau 

 collected by JACOBSON, concluded that wind or air currents are not of 

 such importance. All the Diptera found in 1908, in his opinion, have reached 

 the island probably by sea as tgg, larva or pupa. It is true that the short 

 distances between Krakatau or Verlaten I. and Sebesy, and between Sebesy 

 and Sumatra, will facilitate the dispersal of animals by drifting wood, but 

 this is also favourable for those animals which come to the islands on 

 the wing. 



The north point of Verlaten I. is not more than 15 K.M. from Sebesy, 

 and Krakatau only 19 K.M. The sea between Krakatau and Java or Prinsen 

 Island is about 40 K. M. wide. We need not suppose that the new fauna 

 of Krakatau has come direct from the Sumatra or Java mainland; the 

 animals have arrived rather by way of Sebesy and Sebuku. These latter 

 islands, only partly destroyed in 1883 and more quickly restored, are 

 a suitable halting place for the new fauna on their way to the Krakatau 

 islands. 



The short distances between the islands are easily accomplished by 

 most insects or other flying animals; not only by those which have strong 

 powers of flight or migrate lengthly, like Odonata and Lepidoptera, but also 

 by sluggish flying species. The latter can reach the islands sailing on the 

 wind, just as so many delicate and wingless animals do. In this way very 

 young caterpillars are known to accomplish rather large distances, even 

 more than 20 K. M., as is the case with the caterpillars of the gipsy-moth 

 in the United States. Neither violent winds nor storms are of much importance 

 in this respect but, on the contrary, moderate and constant air curi-ents. 

 Even when the sky was bright and there was only a slight breeze at sea, 

 we often observed insects (dragon flies, butterflies and different species of 

 Diptera) following our motor or rowing boat for quite a distance. 



De Meyere brings forward the Dipteron Plecia as a species which 

 certainly has not come to Krakatau on the wing. I do not think this is 

 impossible, Plecia coming readily to light and being seen often in the 

 evening sailing on its wings. De Meyere stated further that among the 

 Diptera from Krakatau those which are swift of flight and have strong wings, 

 like Syrphidae and Asilidae, have not come first nor are they more abun- 

 dant. The majority of the Diptera collected by JACOBSON are species the 

 larvae of which live in mould and vegetable debris or fungi. Now we must 

 take into consideration that these predaceous flies on arriving at the island 

 will not always find their proper food there, whereas for these scavengers 

 there were, even quite early, plenty of suitable breeding places. Moreover 



