English: Closeup of two colonies of pavement ants (Tetramorium immigrans) battling for territory on a sidewalk in Mount Vernon, Washington state, US in May. The individual ants are about 3 mm long. Tetramorium ants aggressively defend a territory, and in spring when new colonies are establishing their boundaries large battles like this may be seen on sidewalks, leaving thousands of ants dead. Many of the worker ants can be seen in pairs head to head, with their mandibles locked on the heads of their enemy. Alterations to image: improved sharpness slightly using Unsharp Mask filter in Gimp image editor.