Background: Essential oils, obtained from plants, are an alternative for controlling ectoparasites, particularly lice, mites and ticks, due to the problems posed by chemical insecticides, such as insect resistance, environmental impacts and concerns related to human and animal health. This study aims to investigate and compare the insecticidal activity of essential oils from Origanum floribundum and Eucalyptus citriodora against the louse Bovicola limbatus. Methods: The chemical composition of the two oils obtained by hydrodistillation was determined by gas chromatography coupled with mass spectrometry (GC-MS) and a flame ionisation detector (FID-MS). To determine insecticidal activity, the essential oils were tested at different concentrations (0.05–0.8 µL/mL), with mortality recorded after 15 min, 30 min, 1 h, 2 h and 4 h of exposure. Results: A corrected mortality rate of 100% was achieved for concentrations of oregano and eucalyptus essential oils of 0.8 µL/mL and 0.4 µL/mL, respectively. The LC₅₀ values were 0.11 and 0.10 µL/mL for oregano and eucalyptus, respectively, after 2 h of treatment. The LC₉₀ values observed are 0.31 and 0.24 µL/mL for oregano and eucalyptus, respectively. Conclusion: Both essential oils have similar and promising insecticidal potential and could be an alternative to chemical insecticides in a control strategy that is more respectful of human and animal health and the environment.