Dammerman: Fauna of the Krakatau Islands. 85 



Among the insects, we have the wingless females of Miitillidae, which 

 cannot have reached the islands by their own flight. But the male is a 

 strong insect and can fly easily with the female clasped to his thorax, as it is 

 accustomed to do when mating, therefore it may be suggested that the female 

 Mutillids are thus carried to the islands through the medium of the males. 



The other insects of which females or both sexes remain wingless, 

 must have been dispersed by drifting wood or things of a like nature. 

 Only the very young larvae of Psychldae may possibly have arrived sailing 

 on air currents like so many other young caterpillars do. hi the same way 

 very young spiders migrate, and the abundance of this group on the islands 

 is certainly due to this easy means of dispersal. 



Free-living mites and the other Arachnids have probably drifted ashore 

 with vegetable debris; but the very small gall mites may have been f or the 

 greater part dispersed by the wind again, although others may have been 

 introduced with the galls themselves or through the medium of other animals. 



DOCTERS VAN LEEUWEN has found that the proportion of gall mites 

 and gall midges is about the same on Java, whereas on Krakatau it is 18: 8 

 and on Verlaten I. even 12:4. If these animals had reached the islands 

 in their galls by sea it is not clear why mites should predominate. But if 

 we suppose that the majority of these gall-producers have arrived through 

 the air, evidently gall mites carried along by wind could reach the islands 

 more easily than the active flying Diptera. 



The terrestrial Crustacea and Mollusca also, as well as the Vermes, 

 will certainly have come to the islands by ocean currents. But as to the 

 moss fauna, dispersal by air is possible with these very tiny animals. 



Now if we exclude from the table on p. 84 all the above-mentioned 

 animals which possibly have reached the islands by wind or human agency, 

 there still remain a certain number of species which apparently could not 

 have reached the islands by any other means than by drifting wood. For 

 the three islands, Krakatau, Verlaten 1. and Sebesy, we find, then, that this 

 number is 10 ^/o, Q ^/o and 12°/o of the total number of species occurring 

 there, the highest figure being for Sebesy, which is the shortest distance 

 from the Sumatra coast, and the lowest figure for Verlaten I. North, 

 Although the latter island is not farther away from Java or Sumatra than 

 Krakatau, it must be taken into account that this part of Verlaten I. is more 

 recent land, the reoccupation by animals going on there for a shorter time. 



All this proves, I believe, that new land is first invaded by flying 

 animals, drifting wood or plants becoming more important in the long run 

 only, in this connection it is interresting to note that among all the species 

 recorded by JACOBSON in 1Q08 for Verlaten I. there is not one wingless 

 animal. 



According to the above supposition we would expect that the number 

 of wingless animals on Krakatau has also increased since 1908, but computing 

 the figures for the different years, we get 80 ^/o winged animals in 1Q08 



