Yes.
Permethrin, a mosquito insecticide commonly sprayed in residential areas by Colorado cities and counties, can be toxic to pets in high concentrations.
The chemical, also found in some dog flea collars, is approved for use in products in low concentrations — often diluted to 1/100th of a pound with water or oil. Fort Collins, Loveland, Longmont and Broomfield are among the Front Range communities contracted with a mosquito management company that frequently uses a 30% permethrin mixture, applied at no more than .007 pounds per acre.
Exposure to permethrin can cause dogs and cats to act strangely, twitching their ears or rolling on the ground.
Cats are especially sensitive to the chemical. Exposure to concentrations over 45% can affect their nervous system and lead to death. The Fort Collins city website recommends bringing pets indoors during fogging.
Cities and counties usually spray permethrin in July and August when West Nile virus levels spike.
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