The Flowtron Replacement UV Bulb is the main force of attraction for the insects. When the insects come near the bulb, depending on the mechanism of the bug zapper or fly killer, the insects either get zapped and are killed instantly by the nearby non-clogging, high-efficiency shock grid, or stick to the hidden, adhesive fly boards. The UV Bulb enables the Flowtron Bug Zapper and Fly Killer series of products to work continuously to ensure you and your family are safe at all times.