As the region moves toward cooler months, changing weather patterns across the state are affecting mosquito activity levels, according to experts with the University of Florida.
While mosquito activity typically declines once temperatures fall below 50 degrees Fahrenheit, a combination of drought and late-season rainfall has created complex conditions potentially influencing mosquito populations and the spread of viruses.
“Florida’s multiple climate zones allow for a high diversity of mosquitoes,” said Dr. Eva Buckner, an assistant professor at the University of Florida’s Institute of Food and Agricultural Sciences Medical Entomology Laboratory.
Communities along the Interstate 10 corridor have experienced arid conditions ranging from abnormally dry to a severe drought, while some areas along the I-95 corridor have seen a foot or more of rainfall.
Researchers use the Keetch–Byram Drought Index (KBDI) to track soil moisture and dryness levels, which has broad applications in fire weather forecasts, agriculture and other weather-related fields.
When the ground is nearly saturated, a region gets a low KBDI value, while higher values - above 700 - can make an area resemble desert-like conditions.
Based on the latest KBDI map from the Florida Forest Service, Calhoun County currently has the driest soil, with an average value of 676, while Flagler County is the wettest with a value of just 70.
Higher KBDI values typically mean less standing water is available to serve as mosquito breeding grounds, but Buckner said there is more to a drought than meets the eye.
In areas of intensifying drought, animal hosts and mosquitoes tend to congregate around the few remaining water sources, leading to potentially higher transmission rates within local communities.
“In drought conditions, birds and mosquitoes can be concentrated around the same water sources,” said Buckner. “That close proximity can actually increase virus transmission, which can then spill over to humans.”
Additionally, where residents turn to irrigation in drought zones, an item as simple as a bucket or a poorly drained culvert can quickly accumulate enough water to serve as a mosquito breeding site, despite there being little rainfall.
Elsewhere in the state, mostly along the I-95 corridor, the transition from dry conditions in late spring and early summer to heavy rainfall during the late summer and fall has also had a direct impact on the populations of mosquitoes.
In South Florida, residents have reported swarms of Aedes taeniorhynchus, commonly known as the eastern salt marsh mosquito - a species that thrives in brackish water and coastal wetlands.
While it is not a carrier of common diseases such as the West Nile virus (WNV) or Eastern equine encephalitis (EEE), it is notorious for its aggressive bites.
“Because we had drought early in the year, many eggs accumulated in dry soil,” Buckner said. “When the rains finally came, all of those eggs hatched, leading to a population boom.”
But time is running out for quick transitions from one extreme to another, as temperatures across the northern part of the state are regularly reaching the 50s during the overnight hours and most communities have entered their yearly dry period.
“The risk of a widespread disease outbreak is rapidly waning. The 2025 Florida arboviral transmission season is coming to an end. The risk of a widespread outbreak of locally acquired malaria, Eastern equine encephalitis, and St. Louis encephalitis is currently low. The risk of continued local transmission of dengue and West Nile virus is currently moderate,” Jonathan Day, professor emeritus of medical entomology at the University of Florida, stated during a recent weekly analysis.
Sunshine State sees dip in mosquito-borne diseases
Is the lower number of reports linked to the increasing drought, more systematic spraying to target mosquitoes in their juvenile stages, or something else?
Experts say the data is not available to pinpoint any one particular reason and caution that declines in certain diseases may simply reflect natural cycles rather than direct impacts from the climate.
“Mosquito-borne disease transmission is very complex,” Buckner stated. “We have to consider environmental factors, host populations like birds, mosquito numbers and even human behavior.”
Efforts that may sound trivial, such as removing standing water from property and avoiding outdoor activity at dawn and dusk, can be significant enough to reduce infections. But again, similar to changes in the climate, it’s unclear how much these efforts are directly responsible for the reported reductions in recent infections.
Still, entomologists warn that now is not the time to relax preventive measures despite lower transmission rates.
The Centers for Disease Control and Prevention recommends using insect repellent and wearing long-sleeved shirts and pants when venturing into areas where mosquitoes are active.
As of mid-October, the agency reports 1,564 cases of WNV, 2,560 cases of dengue and three cases of EEE across the United States.
