The invertebrates of Krka National Park are relatively poorly studied.
To date, only the beetles (Coleoptera), butterflies (Lepidoptera) and dragonflies (Odonata) have been studied in detail. In the broader Krka River area, 289 species of beetles, about 200 species of butterflies and 34 species of dragonflies have been recorded.
Among the dragonflies found near fast flowing waters, the dark blue males and brown or green females of the beautiful demoiselle and banded demoiselle (Calopteryx virgo and C. splendens) command the most attention. The most common species found near the lake-like sections of the river are the yellowish-brown scarce chaser (Libellula fulva) and scarlet dragonfly (Crocothemis erythraea). In the wetland areas, we find the Thracian emerald damselfly (Chalcolestes parvidens), which is also the only recorded habitat of this species in Croatia.
The emperor dragonfly (Anax imperator) can be spotted near ponds. To date, 40 species of day butterfly have been recorded. Among them are the protected species, swallowtail butterfly (Papilo machaon) and the scarce swallowtail (Iphiclides podalirius), and the Cleopatra (Gonepteryx cleopatra), whose population at Skradinski buk is one of the largest in Croatia. Among the brush-footed butterflies (Nymphalidae), two species are particularly interesting in terms of their characteristics and distribution: the two-tailed pasha (Charaxes jasius), one of Europe's largest butterflies, and the painted lady (Vanessa cardui), which does not winter in Europe. Among the night butterflies, the Hayward yellow underwing (Noctua haywardi), has been observed at Skradinski buk for the third time.
According to the available information, a total of 403 freshwater invertebrate species inhabit the Krka River. The most numerous are the Protozoa with 117 species and the insects (Ephemeroptera, Plecoptera, Odonata, Coleoptera, Trichoptera, Diptera, Hemiptera) with 126 known species. The best studied groups of insects are the rotifers (Rotatoria), bivalves (Mollusca), oligochaetes (Oligocheta) and crustaceans (Crustacea).