said by »www.snopes.com/critters/lurkers/lovebugs.asp :

Love bugs are not the result of a genetic cloning experiment gone wrong, nor were they unwittingly loosed from a research facility charged with studying exotic insects. They also weren't bio-engineered as a natural solution to the mosquito problem. (Love bugs do not eat mosquitos: the adults do not eat at all, and larvae feed on decaying plant material.) These overly amorous critters are native to Central America; the best guess as to how they came to these United States places them as undiscovered stowaways who arrived by ship in Galveston or New Orleans around 1920. They migrated into Florida in 1947 from Louisiana, looked around, liked what they saw, and decided to stay. Their natural capacity for reproduction took care of the rest.