Frequently asked questions
  • Why can't I see any spray or hear any noise coming from the spraying truck when it drives by my home?
    The machines used in spraying are much quieter than they once were.  They are also designed to put out insecticide droplets that are an average of 17 microns in size.  The droplets are small so that they can drift further.  Once the droplets are a few feet from the truck, they spread out and can no longer be seen.
  • Why didn't your crews bring the spraying truck down my street tonight?
    Several factors decide the route our trucks take.  Spray directions are first based on wind readings taken every hour.  For example, if there is a south wind, the trucks will drive along the avenues (instead of the streets) so that the wind could carry the droplets into backyards.  Another factor that is taken into account is the products can not be sprayed within 100 ft. of creeks and rivers.  We may also have residents in the area that have requested we turn off the spray within a certain distance from their homes.
  • Can I eat vegetables from my garden after mosquito spraying takes place?
    We recommend that you wash fruits and vegetables thoroughly before consuming them. The labels for the products used in our spraying state that they "can be applied over specific growing crops and range grasses prior to harvest for the control of adult mosquitoes and biting flies within or adjacent to these areas." Labels and Material Safety Data Sheets are available at
  • I was thinking of purchasing one of those mosquito trapping devices that use carbon dioxide to attract mosquitoes in your yard. Do they really work?
    These devices can provide some degree of protection, but do not rely on them for total control.  Traps used along with source reduction and repellents will provide more relief.
  • What about using bats, birds, plants, fish candles, or bug zappers to control the mosquitoes?
    In general, these things will not provide consistent or effective control of adult or larval mosquitoes.  Birds and bats do consume mosquitoes, but they are opportunists, meaning they eat many different things and consume whatever is most abundant at the time.  But both bats and birds combined still don’t consume enough mosquitoes for you to notice a difference in the mosquito population.  Citronella plants have been shown to be ineffective, and the candles are only slightly better (the light from the flame can actually attract more mosquitoes than it repels).  Bug zappers are not effective in reducing mosquito populations, and can kill great numbers of non-target insects such as moths.
  • Why don't you spray when the weather is cool?
    The product used by Cass County Vector Control must be applied when the temperature is at least 55 degrees and the wind is less than 10 miles per hour. This product thickens when the temperature is below 55 degrees. 
    The mosquito count also plays a role in Cass County's decision of when to apply spray.
  • Can my dog and cat get West Nile Virus?
    Yes, these animals can get the virus if they are bitten by an infected mosquito. It is likely that they will make a full recovery if infected. No specific treatment is available, but veterinarians can treat symptoms of the virus.
  • Can my pet transmit the virus to humans?
    There are no documented cases of animal-to-animal or animal-to-human transmission.

  • Are the pesticides that Cass County sprays to kill mosquitoes safe?
    Permethrin and sumethrin are the main pesticides used for mosquito control by “sprayer trucks” in Cass County.  They have many other uses, too. For example, both are applied to the human head to treat lice and are found in products applied to pets.

    The U.S. Environmental Protection Agency (EPA) licensed permethrin and sumethrin for use in mosquito control after evaluating them for potential human health and environmental effects.

    We feel the benefits of using these products outweigh the limited risks they might pose. Because mosquitoes can transmit the life-threatening West Nile Virus and other illnesses, it’s very important that we control the mosquito population. Permethrin and sumethrin are an effective way to do this.

    To learn more about the EPA approval process for pesticides and mosquito control, visit

  • What is "larviciding"?
    A larvicide is an insecticide used to kill or prevent the growth of mosquito larvae. We use a variety of larvicides in our program, varying from granular form, pellet form and briquet form.  The term larviciding refers to applying these insecticides directly to mosquito breeding sites.

    Larviciding is an effective method for controlling mosquitoes because the mosquitoes are concentrated in a small area.

  • How do officials decide when to spray for mosquitoes?
    The Cass County mosquito control program focuses first on controlling mosquitoes before they mature into adults.  This is accomplished by treating breeding sites with larvicide.  If additional control is necessary, the decision to adulticide is based on analysis of adult mosquito populations, weather conditions, and citizen requests. 
  • How can I distinguish mosquitoes from other insects that look similar?
    Visit this Colorado Web site for a great answer to this question.
  • How long can mosquitoes live?
    Male mosquitoes hatch first and usually live six or seven days.  Female mosquitoes may only live for two weeks in the summer, but with enough food could survive for five months
  • How long can mosquito eggs live?
    Eggs can survive for up to five years. After a female mosquito has taken a blood meal she lays her eggs on or near open water.  She can lay 200-400 eggs at a time.  When conditions are right, the eggs hatch into larvae.  This stage of development lasts 4 to 10 days depending on water temperature, species, and food availability.  The larvae then morph into pupae, which is the final aquatic stage.  From the pupal stage, the adult emerges and rests on the surface of the water until their wings dry and they become strong enough to fly away and feed.

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