When it comes to black flies, there are many types of black flies

After reading Rob Perez’s lighthearted article “Return of the black flies” I felt obligated to add some facts that distinguish black flies from stable flies. Yes, there are plenty of “black flies”, currently estimated at 1 million species and counting in the insect order Diptera, and the fly that Rob mentioned was most likely the stable stable fly but should not be confused with one of thirty species of black flies found in Minnesota

The difference between black flies (Diptera: family Simuliidae) and the stable fly (Stomoxys calcitrans, Diptera: family Muscidae) is immense. Worldwide, over 2,200 species Simuliidae, i.e., Black Flies or Buffalo gnats have been named including over 1,800 species of the genus Simulium. Female black flies feed on the blood of mammals while males feed on nectar and pollinate flowers including those of blueberries. In the tropics, species of Simulium spread River Blindness or Onchocerciasis caused by a parasitic nematode and other tropical diseases. Unlike stable flies, female black flies lay their eggs in fast flowing highly oxygenated rivers and streams, not lakes or ponds.

According to The Pennsylvania Department of Environmental of Protection, the immature stages of black flies are aquatic and exclusively inhabit flowing streams and rivers. They can be found in almost every stream in Pennsylvania, from tiny, cold spring flows to very large, warm rivers. Only streams that are severely impaired by acid mine drainage or pollution will not support black fly populations. However, black flies are not found in lakes, ponds, swamps, and other standing water habitats. Stream flow is essential for transporting food and oxygen to the immature stages.

Stable flies resemble the common house fly but unlike the house fly, Musca domestica, adults have long, bayonet-like mouthparts for piercing skin and feeding on blood. Recent rain however had nothing to do with the emergence of biting stable flies whose populations peak in late summer. The larval habitats of black flies (Simuliidae, well oxygenated running water) and stable flies (Muscidae) (manure) couldn’t be more different. Black fly larvae develop in well oxygenated streams and rivers. Stable flies develop in manure. At this time of year true black flies (Simuliidae) are tiny larvae attached to pebbles and stones by silken threads where they filter out plankton ready to emerge as winged adults next May and June to torment humans and other animals.

David MacLean,
Grand Marais