Protesilaus orthosilaus is a species of butterfly found in the Neotropical realm (the Mato Grosso of Brazil and also Paraguay).

Forewing transparent: hindwing strongly dentate, above also with a median band, the postdiscal band and the black margin merged into a broad marginal band, the yellowish marginal and submarginal lunules smaller.

Paraguay and Gojaz in Brazil; rare.

[2] Formerly believed to be rare, but has now been seen to occur over a very wide area of the Mato Grosso where it can be seen year round in the cerrado.

Males are found in sandy areas and females seek nectar.