Ixodes trianguliceps, parasite of insectivores and rodent mammals seems to be distributed throughout France, except in the mediterranean low altitude areas. This tick which does not manifest any parasitic specificty, has meanwhile preferred hosts (Clethrionomys glareolus, especially). At low altitudes, it likes forests, hedge-rows and heaths and at higher altitudes (Subalpine and alpine), opened area may be densely inhabited. The authors study the numerous concerned vegetal associations and precise the tick's phenology, particularly in the Bas-Dauphiné. They also discuss the many hypothesis concerning the still unknown ecology of I. trianguliceps free instars.