The use of commercial or municipal mosquito spraying creates a conflict between public health and wildlife safety. These applications use broad-spectrum insecticides that do not distinguish between mosquitoes and hummingbirds. The physiological vulnerability of small birds means that even brief exposure to the insecticide mist can have severe, even fatal, consequences. Understanding the specific components of these sprays and the pathways of exposure is the first step in protecting these tiny flyers.
Active Ingredients in Mosquito Sprays
The active ingredients in mosquito fogging operations are neurotoxins targeting the insect nervous system. The two primary categories used are Pyrethrins, derived naturally from the chrysanthemum flower, and Pyrethroids, which are synthetic versions designed to be more stable and potent, such as permethrin, resmethrin, or d-Phenothrin.
These substances work by interfering with the ionic conductance of nerve membranes, prolonging the sodium current in nerve cells. This mechanism causes over-stimulation and hyper-excitability, leading to paralysis and death in insects.
While Pyrethroids are not harmless, their toxicity to small, high-metabolism birds like hummingbirds remains a significant environmental concern.
How Mosquito Sprays Harm Hummingbirds
Harm to hummingbirds occurs through direct contact, inhalation, and ingestion, all of which are amplified by their unique biology. Hummingbirds maintain an extremely high metabolic rate, requiring constant energy intake and a heart rate that can exceed 1,200 beats per minute. This rapid metabolism means they have a high rate of respiration, increasing the risk of inhaling the fine insecticide mist during a spraying event.
The mist is designed to drift and settle, contaminating sugar-water in feeders, bird baths, and flower nectar. Ingesting contaminated nectar introduces neurotoxins directly into the bird’s system. Due to their tiny body mass, exposure to these synthetic chemicals can cause disorientation, slower reflexes, and a reduced metabolic rate, quickly pushing the bird into a severe energy deficit.
Indirect Harm: Loss of Food Source
Beyond direct poisoning, spraying causes significant indirect harm by eliminating the hummingbirds’ primary protein source. Although they are known for nectar feeding, about 80% of their diet consists of small insects and spiders, which are essential for growth and feeding their nestlings. The indiscriminate nature of the sprays eradicates this insect food base, forcing the birds to expend more energy searching for food, which can be devastating during nesting season.
Safety Measures for Bird Owners
Homeowners and residents can take several proactive steps to minimize the risk to hummingbirds when spraying is scheduled in their area.
Protecting Feeders and Baths
The most immediate action is to temporarily remove all hummingbird feeders and bird baths from the yard before spraying begins. If removal is not possible, cover the feeders tightly with a plastic bag or tarp to prevent chemical residue from settling on the feeding ports and in the nectar.
After spraying is complete, thoroughly rinse any outdoor surfaces the birds may frequent, particularly natural flowers and the exterior of feeders, before refilling them with fresh nectar.
Prioritizing Safer Control Methods
Using non-toxic alternatives for mosquito control should be prioritized over broad-spectrum fogging treatments. This includes eliminating all sources of standing water to prevent mosquito larvae development.
Targeted larvicides containing Bacillus thuringiensis israelensis (BTI) are a much safer option. This naturally occurring bacterium is toxic to mosquito larvae but harmless to birds, fish, and other wildlife. If a bird appears lethargic, disoriented, or exhibits tremors after a spray event, contact a local wildlife rehabilitator immediately for specialized assistance.