Residents of Southern California's San Gabriel Valley are facing an unusually severe infestation of tiny black flies, known for biting eyes and leaving itchy red welts. The insects, smaller than mosquitoes, are swarming in numbers far higher than typical for this season, particularly in communities such as Azusa, Altadena, Glendora and San Dimas.
According to the San Gabriel Valley Mosquito and Vector Control District, the flies breed in fast-moving water, such as the San Gabriel River. Unusually warm winter temperatures and increased river flow from early snowmelt have created ideal conditions for rapid population growth, with numbers surging into the hundreds compared to single digits last year.
While the flies do not transmit disease, their bites can be painful and cause allergic reactions in some individuals. Residents report that bites occur even when wearing protective clothing or insect repellent. Officials recommend using DEET-based repellents, wearing light-coloured, loose-fitting clothing, and avoiding peak activity times at sunrise and afternoon.
Control efforts are underway, focusing on treating larvae along waterways. However, adult flies may remain active for several weeks. Homeowners are advised to monitor decorative water features, as flowing water can create additional breeding sites.
