This unique mosquito trap catches only the ones that bite. Particularly effective on the Culex mosquito, the one that spreads west nile virus. The trap works by luring female mosquitoes inside using a pheromone- once inside they cannot escape. Two per average yard will reduce the population significantly. Trap can be rinsed out and reused many times during the season, more bait will be required (SpringStar mosquito refill lure, item S1519). Try it, you"ll like it.