Invertebrates

Of the 2,130 invertebrate species known in Žemaitija National Park, the most abundant is the insect class – 1,864 species. The best studied of these are butterflies and moths (Lepidoptera), with 664 known species, beetles (Coleoptera) – 627 species and True flies (Diptera) – 300 species. The fewest species, 86 each, are from the orders of caddisflies and bees, ants, wasps (Hymenoptera), and 43 from the order of dragonflies and damselflies (Odonata). Other insect orders, such as Heteroptera (True bugs), mayflies (Ephemeroptera) and grasshoppers, crickets (Orthoptera), have been little studied and only a few or a dozen species are known.

26 invertebrate species living in the National Park are included in the Lithuanian and international lists of protected species. The Clouded apollo (Parnassius mnemosyne), typical of the Samogitian region, can be seen as early as May, when the host plant fumewort (Corydalis solida), finish flowering, in Plateliai Manor Park, Šarnelė Mound and elsewhere. Other rare butterflies can be observed in grassland and wetland habitats: old world swallowtail (Papilio machaon), large copper (Lycaena dispar), marsh fritillary (Euphydryas aurinia), scarce fritillary (Euphydryas maturna), the falce heath fritillary (Melitaea diamina), large heath (Coenonympha tullia).  The abundance of protected species is also notable for the Odonata class. Lilypad whiteface (Leucorrhinia caudalis), large white-faced darter (Leucorrhinia pectoralis) green snaketail (Ophiogomphus cecilia), pygmy damselfly (Nehalennia speciosa), green hawker (Aeshna viridis) fly near water bodies.

More than a hundred species of arachnids are spread in various biotopes. The best studied is the order of spiders. 116 species are known, i.e. about a third of all known spiders in the country. A large semi-aquatic spider, the Great raft spider (Dolomedes plantarius), has also been found on the shores of Lake Babrungas, which is able to move deftly on the surface of the water and, if threatened, to submerge itself under water.

84 species of land and water molluscs are known in the national park, of which Geyer’s whorl snail (Vertigo geyeri) and the thick shelled river mussel (Unio crassus) are protected. Pond snails (Lymnaeidae), ramshorn snails (Planorbidae), Anodontas, Dreissenidae family mussels are common in various water bodies of the park. Among the 53 species of land molluscs, one can easily discover the well-known roman snail (Helix pomatia) and other various miniature snails and slugs that leave their slimy tracks.

Crustaceans have not been extensively studied within the park. Crayfish are best known. Since ancient times, the common inhabitant of water bodies in the park has been the european crayfish (Astacus astacus). However, the crayfish plague and other factors greatly reduced their population, so from 2019 the European crayfish has been added to the list of protected species. Instead of of the native European crayfish Lake Plateliai is increasingly inhabited by an invasive spinycheek crayfish (Orconectes limosus) native to North America.