Spring is the prime time for the emergence of Aedes sierrensis, the western treehole mosquito. These mosquitoes lay their eggs in cavities of oak, bay, and several other types of trees. Treehole mosquito larvae can also be found in discarded tires or containers where plant debris and water has accumulated.  Residents living in areas with dense populations of trees, adjacent to recreational areas, or open space may experience large numbers of treehole mosquitoes. They can be aggressive biters during the day and evening. 

While these mosquitoes are currently not known to transmit pathogens to humans, they can cause severe discomfort and transmit canine heart worm to your dog. Contact your veterinarian to discuss heartworm prevention measures.

Ways you can control treehole mosquitoes on your property

• Inspect trees for holes, including holes as small as ½” that lead to cavities that may hold water. Contact a licensed arborist to discuss appropriate measures to prevent water from accumulating in treeholes.
• Remove buckets, toys, tarps or other items holding water.
• Check your gutters for clogs and standing water.
• Contact the District for help reducing mosquito populations on your property.
• For temporary relief from treehole mosquitoes in your backyard, try using one or more oscillating fans pointed away from seating areas. Treehole mosquitoes are weak flyers and have difficulty flying against the wind generated by the fans.