In Costa Rica Lachesis stenophrys is the longest venomous snake reaching approximately a total length of 2.5 m. Its distribution is along the Caribbean versant of Nicaragua to western and central Panama (Campbell and Lamar, 2004), and in Costa Rica is found in tropical and subtropical rainforest on the Caribbean versant. It is an uncommon species even though in certain protected areas remains relatively common (Solórzano and Cerdas, 1986; Zamudio and Greene, 1997). The species of this genus are the only ones in the New World that lay eggs instead of giving birth to newborns with the possible exception of Bothrocophias colombianus (Savage, 2002; Campbell and Lamar, 2004; Solórzano, 2004).