In the Malé Karpaty Mts as well as nearby Trnavská pahorkatina hills the phenology of Chelidurella acanthopygia nymphal instars was studied in the period of 1999-2002. Abundance of the species varied between 1-33 ind.m -2 at the study sites. The first specimens, adults of both sexes from the previous year shortly after their overwintering appeared in the samples already in March. The first nymphal instar (N1) was sampled from the second decade of April till the end of the second decade in June. Interval of their existence took approximately 70 days. The second instar (N2) appeared from May (2nd decade) to the end of July in the period of more than 80 days. The third instar (N3) was recorded in the period of more than 75 days from June (beginning of the 2nd half) to the 1st week of September. The fourth instar (N4) was present from the beginning of July to September (1st decade) (period of more than 70 days). The first new generation adults (females and males) appeared at the end of summer (August). After winter they will form a new parental generation for the next year. The obtained data on the instars N1-N4 and length of their existence in the Malé Karpaty Mts declare that the ontogenesis of C. acanthopygia from the 1st nymphal instar to imago takes 100-120 days.