Pipistrellus hesperus hesperus (H. [Allen])
Western pipistrelle
Scotophilus hesperus H. [Allen], Smithsonian Misc. Coll., 7 (no. 165):43, June, 1864.
Vesperugo hesperus True, Proc. U. S. Nat. Mus., 7:602, 1885.
Pipistrellus hesperus [Miller], N. Amer. Fauna, 13:88, October 16, 1897.
Type.—Obtained at Old Fort Yuma, Imperial County, California, by G. H. Thomas; catalogued in U. S. National Museum on October 31, 1861.
Measurements.—A specimen from Maryhill, Klickitat County, measures: total length 68; length of tail 27; hind foot 7; ear 10; height of tragus 3; weight 4.2 grams. Two males from Vantage, Grant County, average: 68.5; 27.5; 6; 11; 4.
Distribution.—Known only from along the Snake and Columbia rivers of south-central Washington; recorded from Vantage (W.W.D.), south to Maryhill (M.V.Z.), and east to Almota ([Taylor] and [Shaw], 1929: 9).
Description.—This is the smallest bat found in Washington, its body being approximately 1-3/4 inches long and the tail 1-1/4. It may be separated from Myotis by the bent tragus and by the possession of 34 rather than 38 teeth. The dental formula is: i. 2-2/3-3, c. 1-1/1-1, p. 2-2/2-2, m. 3-3/3-3 = 34.
The genus Pipestrellus is cosmopolitan in distribution. The few records for the single subspecies found in Washington indicate that it is a casual, though probably regular, summer visitant from the south.