How Household Pesticides Effect our Wildlife


Question: I have heard about how pesticides effect the environment. How do household pesticides effect wildlife since many homeowners treat lawns and neighborhood ponds?

Answer: Most people know that improper use of pesticides is bad for the environment. Often, the ways poisons reach wildlife and the effects pesticides have on wildlife, directly and indirectly, are not clear to the general public. The effects on wildlife are considered poisoning effects and may be primary or secondary.

Ingestion or contact with a pesticide causes primary poisoning. Keep in mind that a pesticide is any chemical used to control pests. In most cases, primary poisonings are accidental. One problem is the accidental poisoning of pets or wildlife with rodenticides (poisons to kill rodents). Most bait poisons required a tamper resistant bait station or that they be placed in areas inaccessible to children, pets, livestock, and wildlife.

When an insect pest or pathogen attacks our ornamental or food plants we may be inclined to immediately get out the pesticide. All pesticide labels have a section entitled "Environmental Hazards." The environmental hazards section states that the pesticide is toxic to certain animals, has secondary effects on other animals, and if it is toxic to beneficial insects (like bees). It also gives restricted uses. If an active ingredient in the pesticide is toxic to bees then do not spray when the plant is flowering or you may kill bees, butterflies, and other beneficial pollinators. If the plant is an ornamental with fruits or berries eaten by birds, do not treat plants with ripe fruits if they are toxic to birds or other wildlife unless all fruits have been removed first.

Most pesticides warn that they are toxic to fish or other aquatic invertebrates. Be careful when using pesticides near water bodies where runoff will readily carry the toxins into the water. Remember that storm runoff can carry pesticide residues from yards into streets and through storm drains into retention ponds and other bodies of water. If possible, try to find alternative control methods that are not toxic to aquatic organisms.

Secondary poisoning occurs when a predatory animal eats a prey animal that has been poisoned. The most common example is when a hawk, owl, dog, cat, fox, skunk, or any other predatory animal eats a poisoned rodent or pigeon. The problem of secondary poisoning can be reduced by using traps to control nuisance wildlife infestations, systematically collecting and disposing of carcasses when rodenticides are used, or by using poisons that do not cause secondary poisoning (i.e. Cholecalciferol). Birds feeding on poisoned turf insects are another example of secondary poisoning.

Secondary poisoning can also be caused by bio-accumulation. This occurs when small amounts of poison are ingested over time and accumulate in the animalís tissue. One way this can occur is when a bird or mammal feeds on numerous insects treated with an insecticide. Birds and bats accumulate the poisons in their fat. When the birds or bats migrate or hibernate, they use their stored fat as energy and the poison is released into their system. Development of young in mammals and yoking of eggs in birds also causes a mobilization of a motherís fat causing the release of a potentially lethal concentration of pesticide into the motherís system. This is the primary reason why so many insecticides like DDT and chlordane are no longer in use. Some chemical compounds persist in the environment, bio-accumulate, and move up the food chain. Current pesticides are less persistent and are therefore less likely to bio-accumulate. Using Integrated Pest Management techniques will decrease pesticide dangers to all living species.



Shannon L. Ruby is the Natural Resources/Agriculture Agent with the University of Florida/IFAS and Lee County Extension Service. To submit questions, call 461-7515 between 9am and 4pm or send questions to 3406 Palm Beach Blvd. Fort Myers, FL 33916-3736 or via e-mail at