Ridens is a genus of about 20 described species of neotropical skipper butterflies to which we add Ridens conservationinternationalis Burns and Grishin, new species. We describe it from wild-caught caterpillars, what they eat, pupae, reared adults, genitalia, nuclear and mitochondrial genomes, and the Z chromosome. The type-series of this skipper comes from mid-elevation (510–980 m) rain forest on the Caribbean slope of the Cordillera Guanacaste in northwestern Costa Rica. (One male has been taken in Darien in eastern Panama.) To date, caterpillars have been found on just three species in two genera (Persea and Beilschmiedia) of Lauraceae. The head of immature stages is unusual with respect to larval color pattern and pupal morphology. Adult facies differs from those of congeners, and male genitalia differ sharply from those of the other species of Ridens reared in Area de Conservation Guanacaste (ACG). Three phylogenetic trees based on genomic data show that R. conservationinternationalis is well-removed from described species of Ridens but close to a similar-looking male of an undescribed species from Peru. (Tangentially, we undo the polytypic status of R. crison by reinstating R. cachinnans as a species instead of subspecies and newly raising R. howarthi from subspecies to species.)