Although the forest teems with all kinds of insects and other invertebrate fauna, very little information is available on these groups of animals. So far only two groups of insect have been considered in depth viz. mosquitoes  and butterflies. However, the Sinharaja has featured prominently in surveys of Sri Lanka insect fauna conducted by the Smithsonian Institution. It is evident from these studies that there is much scope for detailed investigations of the invertebrates.

                            Studies on the mosquito fauna have shown that at least 27 species have been recorded as adults. The majority, 21 species, were found to breed in surface water sources. The rest used more specialised habitats for breeding. For instance Orthopodomia flavithorax and Culex uniforms breed in tree rot holes filled with water, while C. uniformis and Tripteroides affinis and a few other species use water filled bamboo culms. The most fascinating of all, are the two species Tripteroides dofleini and Armigeres magnus that breed exclusively within the pitcher of Nepenthes distillatoria.

                             The butterfly fauna of the forest has only been listed, and so far 65 species have been recorded in the western sector of the forest. These include 2 endemic species and 19 endemic subspecies (Table 13). Among the common and more interesting butterflies one comes across in the forest are the Tree Nymph, a large black and white butterfly that inhabits the forest canopy, the Common Bird-wing reputed to be the largest butterfly in the country, the Clipper, the Cruiser and the most beautiful of all, the iridescent Blue-banded Peacock. One of the rarest species in Sri Lanka, the Five bar Swordtail, can also be seen during the months of March and April, the season of butterfly migration

Of some 65 butterfly species the Blue Mormom (Papilio crino) is the commonest one recorded in the Sinharaja Forest. The others include two endemic species and 19 endemic sub-species. One of the common and interesting butterflies that one comes across in the forest is the large black and white tree nymph, reputed to be the largest butterfly in the country.

Table 13. A few common and interesting butterflies of Sinharaja.

                 * Endemic species 

                              Of the insects at sinharaja, of species interest are two endemic species of wasps of the family Loboscelidae. They are parasitic on Stick insects. The Sinharaja is the only known location where they have been recorded from the Asian region, the other centres of distribution of this family being New Guinea and Australia.

Giant pill-box millipede (Arthosheaera versicolor)

                              Of the invertebrate forms, the land leech Haemadipsa ceylanica is the one most frequently encountered, a fact that becomes all too evident to any visitor to the Sinharaja. Several other commonly encountered species are worthy of mention; the Giant earthworm (Megascoles coeruleus) at least half a metre in length, and three centimeters in diameter and deep three centimeters in diameter and deep blue in colour, the Giant millipede (Spirostreptus sp.) and the Giant pill-box millipede (Arthosheaera versicolor). One of the commonest spiders encountered is the Giant woodspider (Nephila maculata). The large and beautiful spider seen on the web is the female while the small almost unnoticeable little red spider is the male. Several species of Tarantula (Poccilotheria spp.) are also common in the forest. At night the Scorpion (Heterometrus spp.) can be seen along the logging roads and skid trails.   

Giant woodspider (Nephila maculata)

Forest cricket (Holochlora albiba)