... Theory:By emitting Ultrasonic + Electromagnetic waves, causes a disturbance to bugs, spider and various of pests, consequently forcing them to fly ... spiders away, but can chase various of pest, such as bugs, fleas, crockroaches, silverfish, etc.4. The device is transparent and ... .5x40x30.5CM 20FT' : 39480PCS 40FT' : 80340PCS 40HQ:94200PCS Ultrasonic + Electromagnetic Bugs / Spider Repeller