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Mosquito Traps

The Health Department uses mosquito traps (a gravid trap or black-light trap) at various locations in Halton to monitor mosquitoes for the presence of West Nile virus. Trapped mosquitoes are sent to a lab and tested for West Nile virus.

Image of Black-Light Trap

Why is the Health Department trapping mosquitoes?

  • Mosquitoes feed on birds, so it is possible to find West Nile virus (WNV) in mosquitoes.
  • The mosquitoes caught in traps can be tested to identify the species, count the number of mosquitoes trapped, and identify if any of the mosquitoes are carrying the virus.

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If a trap is in my yard or near my house what should I know?

  • The traps are equipped with a light or a scent that attracts the mosquitoes.
  • The mosquitoes fly into the trap and are held in a net.
  • They are then collected for testing.
  • The mosquito traps encourage mosquitoes to fly to the area of the trap and away from people.
  • Traps are located in places away from areas where people spend their time outdoors, so having a trap near your home attracts mosquitoes away from people and to the trap.
  • Mosquitoes are more likely to fly to a trap than to people, minimizing contact with mosquitoes.
  • The traps are located in an area where mosquitoes are found, such as areas near trees and shrubs.
  • They are located in an area where there is limited access. Health Department staff will monitor and maintain the traps daily.

Image of a Gravid Trap

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How can I protect myself from mosquito bites?

  • You should always take steps to protect yourself and your family from mosquitoes bites by limiting your time outdoors between early evening and early morning, wearing light coloured long-sleeved shirts and pants with a fabric thick enough to prevent mosquitoes from biting, and by using a recommended insect repellent. Shoes and socks are also recommended.
  • For more detailed information, visit our web pages on protecting yourself and your family from mosquito bites and insect repellent (includes info specific to babies, children, pregnant women and breastfeeding mothers.)

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How can I help reduce the number of mosquitoes around my home?

  • Although traps are located in your area, it is still important to remove any potential mosquito breeding sites around your home.
  • Remove or turn over any containers that can hold water, drain pool covers, and change birdbaths weekly. For more information, please visit our web page, Reduce Mosquito Breeding Sites Around Your Home.

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How do the mosquito traps work?

  • 2 types of traps are used:
    • Black-Light Traps use carbon dioxide and a light to attract mosquitoes.
    • Gravid Traps use a small bucket of scented water.
  • A fan in the trap draws the mosquitoes into a mesh holding bag where they are kept alive, as the mosquitoes need be alive to test for WNV.
  • Once in the trap, the mosquitoes are unable to get out.

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What happens to mosquitoes once they are caught in the trap?

  • Each trap is collected and sent to a lab where the mosquitoes are sorted into groups by species.
  • Mosquitoes are separated into pools and the pools are tested for West Nile virus.

What is a pool?

  • From each trap, the female mosquitoes of the species known to carry and transmit WNV are tested in groups of a maximum of 50 mosquitoes. This is called a pool or batch.
  • A pool can be 1 female mosquito or up to 50 female mosquitoes of the same species from the same trap.
  • The pool is then tested for WNV.
  • Positive pools are reported to the health department so that further investigation, surveillance, or education can take place to protect people from WNV.

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