No, Wondercide Flea & Tick Collar doesn't kill fleas or ticks your pet might already have, but it does repel bugs and acts as an added layer of protection. To kill fleas and ticks, use Flea & Tick Pets + Home Spray in addition to the collar.
If you have an active flea infestation, start with a bath using Flea & Tick liquid shampoo, then use Flea & Tick Pets + Home and Flea & Tick Yard + Garden (if you have a yard) as directed to get rid of the issue fast. The collar can be worn while you get an infestation under control and for ongoing repellency for up to 4 months.