Sand flies are also known as "no see 'ums" because they are very small. In addition to having a formidable bite, they can carry diseases which makes them a public health hazard. Sand flies are common to tropical and subtropical climates and the female bites, primarily after dark, to provide sustenance for her eggs. Sand flies can be difficult to totally eliminate, but there are things that you can do to minimise them.
Unclog gutters, dispose of mulch and wood chips, fill in drainage ditches or dispose of planters. Sand flies gravitate to moisture, so the elimination or regular maintenance of these things is essential for minimising infestation.
Avoid wearing cologne or perfume. Sand flies are attracted to the scent of perfume and they are likely to bite you if they land on you.
Screen in your patio if you spend considerable time on it. Do this after you have done everything else to eliminate the sand flies.
Spray the yard with an insecticide, especially after a soaking rain. Sand flies are attracted by moisture, an insecticide will repel them.
Light citronella candles on the patio to repel sand flies when you are in the yard for an extended period of time.
Vacuum your home often during the summer. Dogs and cats are hosts for the eggs of sand flies. When pets come indoors the eggs come with them and they land on floors and carpeting.
If you have a problem with sand flies suggest that guests wear long sleeve shirts and slacks when you plan to entertain in the yard.