The distribution of Ixodes itriae depended upon the density of the nesting birds and the type of substrate. All stages (except eggs) showed an unimodal peak of activity in the last week of June and the first week of July. Newly molted males, nymphs and larvae were recovered in August. Uria aalge was the preferred host of I. itriae although the extent of utilization depends upon the availability of the host. Nymphs require the least amount of time to engorge followed by larvae and females. Feeding sites of all the stages in the laboratory indicate that the head of the host is preferred despite a preference for other body areas in the field. Percentage weight increases of each stage after engorgement indicate that larval weight increases least, followed by females and nymphs. Observations on reproductive behaviour Were made and measurements of a spermatophore given. The oviposition rate and the development of each stage under different temperature and humidity regimes was determined. Details of the life cycle, based on field and laboratory data, are presented.