As the most numerous group of the animal world, insects (Insecta) show their full diversity in the Krka River basin, inhabiting both aquatic and terrestrial habitats.
Research into aquatic insects has recorded fourteen species of stoneflies (Plecoptera), eleven of which are strictly protected, and fifty-eight species of caddisflies (Trichoptera). Of the stoneflies, the most widely distributed species is Isoperla illyrica, endemic to the spring areas of the Dinaric karst.
Attention is attracted to the brightly colored dragonflies (Odonata), with thirty-eight species documented in various types of aquatic habitats. The most prominent among them are the banded demoiselle (Calopteryx splendens) and the blue beautiful demoiselle (C. virgo), found along fast flowing water courses, while the lake-like sections and ponds are most often overflown by the lesser emperor (Anax parthenope), emperor dragonfly (A. imperator), and the goblet-marked damselfly (Erythromma lindenii).
Of terrestrial habitats, grasslands are ideal habitats for butterflies, grasshoppers, praying mantises, and crickets. There are eighty-one species of day butterflies, and the most numerous is the gossamer-winged family (Lycaenidae). In the white and sulfur family (Pieridae), the cleopatra (Gonepteryx cleopatra) stands out, whose population in the area of the Skradinski buk waterfall is one of the largest in Croatia. Twenty-two species of grasshoppers were found, fourteen species of crickets, and three species of praying mantises, the most common of which is Mantis religiosa.
The fauna of beetles is also rich and diverse, and the most numerous are those from the families of ground beetles (Carabidae) and diving beetles (Dytiscidae). Two subspecies of the ground beetle, Carabus caelatus dalmatinus and Palaeostigus ruficornis dalmatinus, are Dalmatian endemics.
