Killer Flies by Mark Kendall

The population is being eaten up alive--in a harrowing novel of flesh-creeping horror...

First they feasted on farm animals. Then they found humans...

A little girl was dead, attacked and mutilated by some things, creatures of nightmare that were spreading outward like the Black Death, stripping entire towns bare of life.

The death toll mounted, with bodies maimed or ripped to shreds, and thousands cowered in the shadows, hiding fearfully from the death out of the skies, the millions of sucking probosci eagerly reaching out for the attack. And terror erupted into uncontrollable panic, as a lone scientist worked feverishly to save a dying population and destroy the KILLER FLIES.

...

Swarms of carnivorous flies terrorize a small New Mexico town and the scientist responsible for the insects' creation must find a way to stop them before the Air Force is allowed to take more drastic measures.