Mirocastnia smalli is a moth in the Castniidae family. It is found in Panama. The habitat consists of a forest with Colpothrinax cookii palms, several moss covered trees and Bromeliaceae species.
The length of the forewings is 21.5âÂÂ26 mm for males and 19.5âÂÂ29 mm for females. Adults are on wing from March to August. They mimic Pythonides limaea.
The species is named for Gordon B. Small, who first collected the species.