[3][4] Common names for L. melanocephala include black-headed bushmaster,[5] as well as cascabel muda ("silent rattlesnake") and matabuey in Spanish.

Adults of L. melanocephala frequently grow to 1.9–2 m (6.2–6.6 ft) in total length (including tail).

L. melanocephala is found in Costa Rica on the Pacific versant of southeastern Puntarenas province from near sea level to about 1500 m (about 4,900 feet).

The type locality given is "tropical rainforest 9 km northern of Ciudad Neily in southeastern Provincia de Puntarenas, Costa Rica.

"[2] Campbell and Lamar (2004) describe its range as southwestern Costa Rica and possibly extreme western Panama, but state that almost all locality records are from Puntarenas province.