Key to the Grass Skippers (Hesperiinae) of the Pennsylvania and Neighboring States

Corey Husic (July 8, 2011): A dichotomous key to the grass skippers (Hesperiinae) of Pennsylvania. It should work for the common species in many adjacent states as well.

A. Underside of hindwing is plain (includes dusting and pale veins with plain background color)
- B. Underside of hindwing is orange
  - C. Leading margin of forewing is brighter orange [Crossline Skipper]
  - C. Leading margin of forewing is same color as hindwing
    - D. Upperside of wing is primarily orange; white border on wings [European Skipper]
    - D. Upperside of wing shows a significant about of black
      - E. Very small; when sitting with wings closed, forewings only minimally extend past hindwing [Least Skipper]
      - E. Fairly large; when sitting with wings closed, forewings extend well past hindwing when sitting [Delaware Skipper]
- B. Underside of hindwing is brown
  - F. Underside of hindwing very dark with white dusting on back edge
    - G. Small; white, triangular spot near tip of forewing [Common Roadside-Skipper]
    - G. “Bandit mask” on face and white basal dot visible on underside of hindwing [Dusted Skipper]
  - F. Underside of wings lighter brown without distinct dusting
    - H. Veins on underside of hindwing paler than background color
      - I. White line along bottom edge of underside of hindwing [Two-spotted Skipper]
      - I. Underside of hindwing yellow-brown; white line absent from bottom edge [Swarthy Skipper]
    - H. Veins on underside of hindwing same color as background color
      - J. Leading margin of forewing is distinctly brighter orange than underside of hindwing
        K. Strong contrast between forewing margin and underside of hindwing; male’s stigma parallel to top margin of forewing [Tawny-edged Skipper]
        
        K. Weak contrast between forewing margin and underside of hindwing; male’s stigma skewed in comparison to top margin of forewing [Crossline Skipper]
      - J. Leading margin of forewing not distinctly different
        M. Upperside of forewing entirely plain brown [Dun Skipper]
        
        M. Upperside of forewing with large, rectangular white patch; white patch below antennae clubs [Little Glassywing]
A. Underside of hindwing is patterned
- N. Pattern on hindwing made up of a few small, white dots
  - O. Lower dots in line, with top dot pushed inward [Crossline Skipper]
  - O. Lower dots misaligned, sometimes in the shape of a “3” or backwards “3” [Little Glassywing]
- N. Pattern on underside of hindwing not made up of small, white dots
  - P. Underside of hindwing gray-dusted with white spots [Pepper-and-salt Skipper]
  - P. Underside of hindwing not dusted
    - Q. Underside of hindwing brown with ONE main, light-colored ray extending outward
      - R. Ray distinct; faint, light-colored spots above and below band [Broad-winged Skipper]
      - R. Ray on underside of hindwing faint against background color [Dion Skipper]
    - Q. Underside of hindwing with more than one distinct light-colored band or a different pattern
      - S. Underside of hindwing yellowish with faint pattern
        T. Underside of hindwing with scattered black dots [Fiery Skipper]
        
        T. Underside of hindwing with chevron-shaped pattern
        U. Stigma very large and squarish; small dark spot at bottom of underside of hindwing [Sachem, male]
        
        U. One spot of “chevron” sticks out towards wing margin [Indian Skipper]
      - S. Pattern on underside of hindwing distinct
        V. Underside of hindwing mostly yellow with small, darker spots [Zabulon Skipper]
        
        V. Underside of hindwing with chevron-like pattern or spot band
        W. Center spot of spot band or chevron in line with lower spots
        X. “Cobwebby” lines connecting spots of chevron [Cobweb Skipper]
        
        X. Short bands make up “spot” band; dark area inside chevron [Long Dash]
        
        W. Center spot of spot band or chevron juts or extends outward or inward
        Y. Center spot of band or chevron juts or extends inward
        Z. Pattern on underside of hindwing resembles airplane [Mulberry Wing]
        
        Z. Pattern does not resemble airplane
        AA. Underside of hindwing rusty yellow-brown with fairly large yellow spot band; appears as though two spots of spot band extend inward [Black Dash]
        
        AA. Underside of hindwing orange-brown with dull (or “blurry-edged’) spot band; leading edge of forewing brighter orange [Northern Broken-Dash]
        
        Y. Center spot of band or chevron juts or extends outward
        BB. Primary color of underside of hindwing reddish-brown with bright white spot band [Leonard’s Skipper]
        
        BB. Primary color yellow and/or brown
        CC. Brown with white spots [Sachem, female]
        
        CC. Brown with yellow spots/patches
        DD. Large yellow blotches on basal area of underside of hindwing [Peck’s Skipper]
        
        DD. Basal area of underside of hindwing with only a small yellow dot [Hobomok Skipper]