Dog day cicada (Tibicen canicularis)
Growing up in Kentucky and Indiana, I saw one or two of the big “cycles” of the 17-year cicadas. Those periodical cicadas don’t live in Florida, but here we get serenaded each summer by a variety of annual cicadas which brood every year.
The dog day cicada (Tibicen canicularis or Neotibicen canicularis, depending on whom you ask) is one of Florida’s 19 annual cicada species. Cicadas are easy to hear but hard to find in the trees, so many entomologists have learned to distinguish different species by the sound of their songs. They can even be identified by what time they sing, as not all cicadas appear at the same time of year. The “dog day” cicadas (there are multiple species) tend to sing in the later, “dog days” of summer, hence the common name. Other common names include heatbug, harvestfly, or dog-day harvestfly.
The song of the dog day cicada has been described as a high-pitched whining drone which lasts about 15 seconds, reminiscent of the sound of an electric saw. The sound is produced by a pair of structures on the sides of the abdomen, called timbals (or tymbals). Only the males have these structures; females are mostly mute. Adults are typically 27-33 mm long. Both adults and nymphs feed solely on tree sap (xylem), and are harmless to humans and to gardens.
Dog day cicada (Tibicen canicularis) 
Dog day cicada (Tibicen canicularis)
Eggs are laid in trees; when they hatch, the young nymphs fall to the ground and burrow downward, sometimes as far as several feet over time. They find a tree root to feed upon, and wait to emerge and molt into an adult, leaving their shells behind clinging to vegetation. This process may take a year in many species, or up to the famous 13 to 17 years of the periodical cicada (Magicicada sp.).
The University of Florida has an excellent guide to Florida cicada species.