To lay eggs female day-biting mosquitoes require blood for nourishment, which they get from humans and animals. They then look for wet places to create the nest. The UP trap mimics their preferred environment through water, attractant and/or pesticide strip added to the container. Attractants have such composition that mosquito's senses confuse it with a host and fly right to it. When the insect gets into the trap through the inner funnel, it cannot escape and stays entrapped inside. If you use the UP trap as an ovitrap, mosquitoes and their eggs die from the lack of nourishment. When you add attractant or pesticide to the container, aka using it as a kill trap, then pests get poisoned and die off quickly.