Abstract
Between 1993 and 2024, a total of 274 hard ticks (Ixodidae) were collected from 138 subterranean localities in Croatia. This study represents the most extensive survey of hard tick fauna in subterranean habitats in Croatia to date. The collected specimens were classified into three genera and seven taxa, including two taxa that could not be identified to the species level (one from the genus Ixodes and one from Haemaphysalis). The genus Ixodes was the most abundant, comprising five taxa, whereas Haemaphysalis and Hyalomma were each represented by a single taxon. The highest diversity of hard ticks was recorded in subterranean habitats in Dalmatia, followed by north-western Croatia and Slavonia. Ixodes vespertilionis Koch, 1844 was the dominant species in the collected sample, representing 81.0% of all specimens, and was recorded in all studied regions. This species was present throughout the entire year, whereas I. hexagonus Leach, 1815 was recorded during nine months, I. frontalis (Panzer, 1798) during four months, and the remaining taxa during shorter periods. The largest number of I. vespertilionis specimens was collected in spring (33.2%), while the lowest number was recorded in winter (16.6%). The record of I. frontalis represents the first documented occurrence of this species in subterranean habitats in Croatia.