We confirm reports from the 20^th century literature that Loxomorpha flavidissimalis (Grote, 1878), the cactus webworm, occurs in southern Texas and northeastern Mexico, and we report and verify for the first time that it occurs in the state of Tamaulipas as an herbivore of the cultivated cactus Opuntia ficus-indica (L.) Mill. var. Copena V-1 (green vegetable). Four cultivated cactus varieties (VALTIERRILLA, COPENAV-1, JALPA and VILLANUEVA) were monitored for four years (from planting to adulthood) (2010–2014). Of the four varieties assessed, only COPENA V-1 showed L. flavidissimalis presence and herbivory. Larvae were observed during the months of March to November, and young cladode losses were attributable to L. flavidissimalis. The cactus webworm represents an additional potential pest for the production of cultivated cactus in Tamaulipas where damage was observed to be 3.7% of the annual yield.