Photo of the Day 39

Midges in Cueva de Villa Luz, Mexico, 2001

Photograph by Stephen Alvarez

Millions of iridescent-winged midges like these throng the inky depths of Cueva de Villa Luz cave in southern Mexico. Hydrogen sulfide, which is poisonous to humans, permeates the cave's walls, streams, and air, sustaining a rich variety of bizarre organisms. Midges, bats, spiders, mites, amblypygids, and small, hemoglobin-rich fish thrive in the sulfur-saturated environment.

(Photo shot on assignment for, but not published in, "Deadly Haven," May 2001, National Geographic magazine)