The invertebrate fauna is poorly studied. There are between 2475 and 2600 identified species, including 1703 insects, but their actual number is estimated to be 6500-7000. The main hotspots are Rila Monastery Forest Reserve, the area around the Fish Lakes to the east and the Kalin reservoir, as well as the areas around the river Radovichka and Bukovo bardo. There are 96 rare, 85 endemic and 146 relict species; 116 are included in worldwide or European lists of endangered animals. Some of the endangered species include beetles: Calosoma sycophanta, Carabus intricatus, Morimus funereus; net-winged insects: Libelloides macaronius; ants: Formica lugubris, Formica pratensis, Formica rufa; butterflies: Parnassius apollo, Parnassius mnemosyne, Euphydryas aurinia, Polyommatus eroides, Apatura iris, Carterocephalus palaemon, Colias caucasica, Erebia rhodopensis, Charissa obscurata, Limenitis populi, Melitaea trivia, Zerynthia polyxena, etc.