A photo of an assassin bug nymph (Reduviidae). The ability of the nymphal instars of several species of triatomine bugs to cover their bodies with dirt or other materials by throwing fine particles on their backs with the 3rd pair of legs (camouflage phenomenon) has been investigated in 21 species or subspecies of these insects. All nymphal instars of Triatoma dimidiata, T. d. capitata, T. plyllosoma, T. maculata, T. vitticeps, Panstrongylus megistus and P. herreri exhibited a high instinctive camouflaging activity. In other species this instinct is more pronounced in one or more of the nymphal instars than in the others. It may be present only in the first instar as in the case of Dipetalogaster maximus. The instinct was absent in T. barberi, T. sinaloensis, T. protacta navajoensis and in 4 species of Rhodnius. T. dimidiata, T. phyllosoma, T. Spinolai and P. herreri were the most effective species in covering themselves with dirt over the entire body.