Castolus is a genus of assassin bugs in the family Reduviidae. There are about 16 described species in Castolus.

Species: These 16 species belong to the genus Castolus:

• Castolus annulatus Maldonado & Brailovsky, 1992-01
• Castolus bicolor Maldonado, 1976
• Castolus bolivari Brailovsky, 1982
• Castolus ferox (Banks, 1910)
• Castolus fuscoapicatus (Stål, 1860)
• Castolus lineatus Maldonado, 1976
• Castolus multicinctus Stål, 1872
• Castolus nigriventris Breddin, 1904
• Castolus pallidus Maldonado, 1976
• Castolus pecus
• Castolus plagiaticollis Stål, 1858
• Castolus rufomarginatus Champion, 1899
• Castolus spissicornis (Stål, 1860)
• Castolus subinermis (Stål, 1862)
• Castolus tricolor Champion, 1899
• Castolus trinotatus (Stål, 1866)