While looking up information on the hairy wood ants, Formica lugubris, I found out about some tiny ants called guest ants that also live in the wood ants' towering mounds. The shining guest ant, Formicoxenus nitidulus, forms a small nest within the bigger nest. As you can see from the photo below, they are called shining because of their reflective, shiny exoskeleton.
The shining guest ant workers are thought to pick up or steal food from their hosts, which are remarkably tolerant of this behavior. When a worker wood ant does attack a shiny guest ant, it usually gives up quickly. Researchers Martin, Jenner and Drijfhout think this is because shiny guest ants smell/taste bad.
Imagine guests that steal your food, take advantage of your security system, and are covered with an unpleasant substance. At least they are cute.
Seriously, ant mounds house a variety of creatures. With the existence of hairy wood ants threatened, the guests become endangered right along with their ant hosts.
Martin, S. J., E. A. Jenner and F.P. Drijfhout. 2007. Chemical deterrent enables a socially parasitic ant to invade multiple hosts. Proc. R. Soc. B 7 vol. 274 (1626): 2717-2722.
For additional photos including a size comparison, see
The Highland Biological Recording Group