English: Two colonies of pavement ants (Tetramorium immigrans) battling for territory on a sidewalk in Mount Vernon, Washington state, US in May. 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. On magnification, many of the worker ants can be seen in pairs head to head, with their mandibles locked on the heads of their enemy. There is a line of ants leaving to the left along the sidewalk edge, so presumably one of the nests is in that direction. When I returned to the spot a few hours later, no ants could be seen.