Johnson's Fly Strike Protector provides lasting protection against Fly Strike for Rabbits and Guinea Pigs over 4 weeks of age. Blowfly Strike (Lucillia sericata) is usually caused by faeces sticking to the rear end of the animal, which attracts flies to lay their eggs. If your pet is already infested with maggots, you should seek veterinary help immediately. Any delay is likely to result in the pet's death. This product is a preventative, not a treatment.