Southern fire ants
A colony of southern fire ant (Solenopsis xyloni) is preparing nuptial flights of winged individuals. This large colony in my backyard shows this characteristic behavior (e.g., many workers come out from the nest and move around on the surface of the ground, winged females and males come out from the nest and get ready for flight, etc.) in later afternoon or evening. They show this behavior for several days in a row. I see the winged females typically climb up to the nearby vegetation. For male, this "climbing" behavior seems to occur much less often. The picture was taken on July 16, 2018 in Riverside, CA.