The essential oil of Deverra scoparia Coss. & Durieu was investigated for its acaricidal activity against the worldwide pest twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). The essential oil was analyzed by fast gas chromatography (GC) and GC-mass spectrometry. The activities of its individual and blended constituents were determined. Our study showed that female mortality increased with increasing D. scoparia oil concentrations, with LD₅₀ and LD₉₀ values at 1.79 and 3.2 mg liter^-1, respectively. A reduction in fecundity had already been observed for concentrations of 0.064, 0.08, and 0.26 mg liter^-1 D. scoparia essential oil. Ten major components, comprising 98.52% of the total weight, were identified; α-pinene was the most abundant constituent (31.95%) followed by sabinene (17.24%) and Δ3-carene (16.85%). The 10 major constituents of D. scoparia oil were individually tested against T. urticae females. The most potent toxicity was found with a-pinene, Δ3-carene, and terpinen-4-ol. The presence of all constituents together in the artificial mixture caused a significant decrease in the number of eggs laid by females, at 0.26 mg liter^-1 (11 eggs), compared with the control (50 eggs). The toxicity of blends of selected constituents indicated that the presence of all constituents was necessary to reproduce the toxicity level of the natural oil.