Western pygmy blue (Brephidium exile)

GenusBrephidium (1)
SizeWingspan: 1.2 - 2 cm (2)

The western pygmy blue has yet to be classified by the IUCN.

The smallest butterfly in the USA, the tiny western pygmy blue (Brephidium exile) is notoriously difficult to find, but is certainly worth searching for as it is beautifully patterned with delicate markings (3). The wings of this alluring butterfly are copper brown, marked with dull blue on the upper-sides, and flecked with white on the underside of the hindwings. The wings are also fringed with white, and there is a row of black spots on both the outer margin and near to the base. The western pygmy blue begins life as a yellow-green caterpillar spotted with tiny brown tubercles (4) (5).

Only occurring in North America, the western pygmy blue ranges from the Texas coast, northwards into the central states and to the western coast of the USA (2).

The western pygmy blue occurs in alkaline habitats such as deserts and salt marshes (2).

Between May and November, the male western pygmy blue defends a small territory, and spends much of its time searching for receptive females. After mating, the female western pygmy blue lays the eggs on the leaves of a saltbush species (Atriplex spp.) (2). The eggs hatch into caterpillars which form a symbiotic relationship with ants (Iridomyrmex species), for which the caterpillar provides food in the form of a nectar liquid whilst gaining protection from the ants in return (6) (7). Once the caterpillar is fully grown, it will pupate to form a loose cocoon, and then undergoes metamorphosis before emerging as an adult butterfly (8).

A weak flier, the western pygmy blue flies close to the ground, and is restricted by its short proboscis to collect the nectar from small flowers. The caterpillar feeds on all parts of the host plant (3).

There are no known threats to the western pygmy blue.

There are no known conservation measures targeting the western pygmy blue.

For more information on butterfly conservation, see:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. ZipcodeZoo (May, 2009)
  2. Butterflies and Moths of North America - Western pygmy blue (December, 2010)
  3. Phillips, S.J. and Comus, P.W. (2000) A Natural History of the Sonoran Desert. University of California Press, California, USA.
  4. Tveten, J.L. and Tveten, G. (1996) Butterflies of Houston and Southeast Texas. University of Texas Press, Texas, USA.
  5. Opler, P.A. (1998) Eastern Butterflies. Houghton Mifflin Company, New York, USA. 
  6. Art Shapiro’s Butterfly Site - Western pygmy blue (December, 2010)
  7. Atsatt, P.R. (1981) Lycaenid Butterflies and Ants: Selection for Enemy-Free Space. The American Naturalist. 118(5): 638-654
  8. O’Toole, C. (2002) The New Encyclopedia of Insects and their Allies. Oxford University Press, Oxford, UK.