Black Fly
Simulium sp.
Observed at Sycamore Canyon on the west side of the Mazatzal Mountains, Maricopa Co., Arizona, USA. 16 May 2010. Length is about 2.5 mm.
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Observed on a submerged rock at Fish Creek, Superstition Mountains, Maricopa Co., Arizona, USA. February 2009. The worm-like larvae cling to rock surfaces in the current by the posterior.
Mountain streams very often support populations of black flies. Although seen as an annoyance by outdoorsmen we must appreciate the fact that their presence generally indicates clean, oxygenated water. The larvae cling to rocks in the current where they extend basket-like mouthparts that filter food particles out of the flow. Thus the activity of black flies also helps improve the clarity of the water. In Arizona's sycamore canyons black flies are often present, but they are not, in my experience, aggressive biters.