68 Treubia Vol. HI, l. 



As to the insects, only general remarks can be made, the great bulk of 

 the material being still undetermined. 



On Krakatau 441 species of insects altogether have been found; on 

 Verlaten I. 238. These two islands have only 114 species in common, one 

 fifth of the total for both islands. This proves, I think, that we either caught 

 only a small part of the total num.ber of species present or that the general 

 conditions on the islands are rather divergent. Now the whole northern 

 part of Verlaten !, where nearly all the collecting has been done, is new 

 land clad with a vegetation somewhat different from that on Krakatau. 

 Owing to this difference we surmise that the insect fauna on both islands 

 is also disparate. But the first mentioned factor is also of importance. 

 One will find, especially in the tropics, every time different species 

 on the same spot, and many of those formely caught are not to be 

 found again. 



Although the total number of insects on Krakatau has been tripled since 

 1QC8, of Hymenoptera only 66 species were collected here in 1920 — 1921, 

 and 28 on Verlaten I., against 8 on the latter island and 51 on the 

 former in 1908. 



Of Hymenoptera parasitica the double number has been obtained on 

 Krakatau, but on Verlaten I. only 2 species were collected, JACOBSON 

 mentioning 4 species. One would suggest that this small number of parasitic 

 insects on Verlaten I. North is due to the recentness of this part of the island, 

 the hosts arriving here first without their parasites. But on Sebesy, where 

 the vegetation is far in advance of that of Krakatau, we collected also no 

 more than 3 parasitic Hymenoptera. So the above suggestion cannot be correct. 

 Also worth mentioning are three species of fig insects found on Karakatau 

 and Verlaten I. ; JACOBSON does not record these insects. Did not the fig 

 trees produce at the time of his visit or could they do so only after the 

 arrival of these small insects, which perhaps took place after 1908? Nowadays 

 all fig trees on the islands abound with fruit and in nearly every ripe fig 

 one will find the insect. 



hi 1908 ants were very abundant on Krakatau and a great nuisance, 

 in 1920 — 1921 the number of species had increased only a little; but the 

 number of individuals seems to be decreasing, except in the glagah fields 

 where they are still annoying. The decrease of specimens is apparently due 

 to the superseding of the grassy plains by the woods. 



The number of Coleoptera, however, has greatly advanced; from 

 23 for Krakatau in 1908 it went up to 115 in 1920 — 1921; for 

 Verlaten I. these numbers are resp. 2 and 68. One of the causes of 

 this increase, as already mentioned, is the practice of sifting. A special 

 study has been made of the soil and surface fauna, and a great many 

 insects and other animals could be collected in this way. Nearly half 

 the total number of beetles has been caught by sifting, as appears from 

 the following list: — 



