What You Need to Know About Black Flies 🔊

They are naturally occurring in flowing water: fountains, rivers, ponds, streams, cascades, & irrigation ditches

They fly in great numbers 😲

They bite around the eyes 👀 & neckline of humans & domestic animals 🐕🐈

Their bites are painful😖, but they do NOT transmit diseases in LA County 

What You Can Do 

Wear repellent on exposed skin to stop the bites (best is a repellent containing DEET) 👍🏾

Turn OFF personal water features for 24 hours once a week 

** Don't forget to turn water back on to prevent mosquitoes 🦟using the stagnant water .

Vector Control’s Role in Reducing Black Flies

Black flies are a persistent biting nuisance in our foothill communities, particularly in areas like Altadena, Azusa, Bradbury, Duarte, Glendora, Monrovia, San Dimas, and Sierra Madre. To help reduce their impact, our agency routinely monitors and treats known black fly breeding sites in public spaces, such as rivers, streams, and other accessible locations like Morris Dam. The District also routinely traps black flies in the foothill communities to monitor the population count and species. This helps the district determine the treatment frequency.    

Since black flies grow in running water, new sources, whether from scheduled dam releases or unmaintained features like decorative fountains and backyard waterfalls, can quickly become hotspots for activity. Our team remains vigilant in identifying and managing these potential breeding sites to help protect our communities.

Protecting Yourself from Black Flies

Black flies can be challenging to avoid, especially in areas with dense vegetation or during peak activity times. To minimize bites:

• Choose open, sunny areas whenever possible, avoiding lowlands or densely vegetated spots.
• Stay indoors during dawn and dusk when black flies are most active.
• Opt for light-colored clothing, as black flies are less attracted to bright colors.
• Cover exposed skin with long-sleeved shirts, long pants, socks, and hats.
• Consider using a head net, available at outdoor and gardening stores.
• Apply insect repellent containing DEET to further deter black flies.

Black Fly Life Cycle

1. EGGS - The female deposits 200-500 fertilized eggs in or on flowing water.
2. LARVAE - Larvae emerge and attach themselves to rocks or foliage under the water and feed on organic debris that flow by. They grow to about 1/4 inch when fully developed. This takes from 10 days to several months, depending on the species and the water temperature. 
3. PUPAE - They then enter the pupal stage, where transformation to the adult stage takes place. 
4. ADULT - Adults will emerge from the pupal case and float to the surface inside a bubble of air.