Black mosquitoes in the left eye may be caused by physiological factors, flying mosquito syndrome, retinal detachment and other reasons. 1. Physiological factors: eye fatigue caused by long time browsing cell phone or computer screen, staying up late, etc. Eye fatigue may cause blurred vision, manifested by black mosquitoes in the left eye. 2. Flying mosquitoes: caused by vitreous liquefaction, you can see small floating black shadows in front of your eyes, similar to black mosquitoes, especially in the white bright background, the symptoms are more obvious, accompanied by a sense of flash. 3. Retinal detachment: retinal detachment due to vitreous pulling, early onset of floaters in front of the eyes, flashing sensation, can be seen in front of the eyes similar to the phenomenon of “black mosquitoes”. Black mosquitoes in the left eye, through the rest and self-regulation did not see significant improvement, timely to the hospital, improve the examination, clear the cause of the disease to give targeted treatment.