other hand, however, we have to consider that the dispersion and migration of
insects is much more easily effected than that of mammals or even of birds.
They are much more likely to be carried away by violent winds; their eggs may
be carried on leaves either by storms of wind or by floating trees, and their
larvae and pupae, often buried in trunks of trees or enclosed in waterproof
cocoons, may be floated for days or weeks uninjured over the ocean. These
facilities of distribution tend to assimilate the productions of adjacent lands in
two ways: first, by direct mutual interchange of species; and secondly, by
repeated immigrations of fresh individuals of a species common to other islands,
which by intercrossing, tend to obliterate the changes of form and colour, which
differences of conditions might otherwise produce. Bearing these facts in mind,
we shall find that the individuality of the insects of Celebes is even greater than
we have any reason to expect.
For the purpose of insuring accuracy in comparisons with other islands, I shall
confine myself to those groups which are best known, or which I have myself
carefully studied. Beginning with the Papilionidae or Swallow-tailed butterflies,
Celebes possesses 24 species, of which the large number of 18 are not found in
any other island. If we compare this with Borneo, which out of 29 species has
only two not found elsewhere, the difference is as striking as anything can be. In
the family of the Pieridae, or white butterflies, the difference is not quite so
great, owing perhaps to the more wandering habits of the group; but it is still
very remarkable. Out of 30 species inhabiting Celebes, 19 are peculiar, while
Java (from which more species are known than from Sumatra or Borneo), out of
37 species, has only 13 peculiar. The Danaidae are large, but weak-flying
butterflies, which frequent forests and gardens, and are plainly but often very
richly coloured. Of these my own collection contains 16 species from Celebes
and 15 from Borneo; but whereas no less than 14 are confined to the former
island, only two are peculiar to the latter. The Nymphalidae are a very extensive
group, of generally strong-winged and very bright-coloured butterflies, very
abundant in the tropics, and represented in our own country by our Fritillaries,
our Vanessas, and our Purple-emperor. Some months ago I drew up a list of the
Eastern species of this group, including all the new ones discovered by myself,
and arrived at the following comparative results:—
Species of Species peculiar to Percentage
Nymphalidae. each island. of peculiar Species.
Java..... 70...... 23.......... 33
Borneo.... 52...... 15.......... 29
Celebes ... 48...... 35.......... 73The Coleoptera are so extensive that few of the groups have yet been carefully