Halogenated monoterpenes isolated from the red alga Plocamium cartilagineum aegypticus , proved their efficacy as acaricide. Both of Violacene and Mertensene, were adulticides with LC50's, 340.56 ppm and 759.23ppm, respectively, against the cattle tick; Boophilus annulatus adult females. Moreover, they can be used as ovicides. Violacene and Mertensene caused reduction in the hatchability by 96.77% and 95% respectively. Clinico-pathological studies were carried out and showed that Plocamium extract is safe to the host and none-target animals.