Four species of mosquitoes have been found to be naturally infected with West Nile virus in Colorado:

• Culex tarsalis
• Culex pipiens
• Aedes vexans
• Culiseta inornata

Culex tarsalis is considered the primary vector of West Nile virus to humans in Colorado

Pictures from CDCs Public Health Image Library

Basic facts about Culex tarsalis in Colorado

• The mosquito is found in the eastern plains, along the Front Range, and in river valleys in the western part of the state
• Exposure to this mosquito can occur in many environments because it breeds in almost any source of standing water including:
  
  • Lakes and ponds
  • Water filled areas occurring along rivers, streams and irrigation canals
  • Water filled areas in irrigated fields or backyards
• Peak numbers of Culex tarsalis typically occur from June-September (especially July-August)
• The risk of bites by Culex tarsalis is greatest at dusk and dawn. Remember that when grilling in the backyard at night