In some areas it is present all year long. In South Carolina, population peaks have been recorded in late July, late September, and late October, but large numbers have been found in Florida between April and November. Overall, Florida has 18 different black fly species, the most common with populations present from August through July. Only female black flies feed on blood. Males feed mainly on nectar.
Black flies can occur in enormous numbers.
Immature stages develop in oxygenated water sources, therefore adults are usually associated with slow moving streams, creeks, or rivers where the immature stages develop. Flowing water does not necessarily imply white water rapids, but water must be moving. Water in lakes and ponds that is not flowing is unsuitable for black fly development. S. slossonae prefers fairly small, slow moving streams with an average velocity of 1.5 ft per second. S. slossonae makes good use of temporary streams that flow seasonally.