Not only are wood ants fascinating and beautiful insects in their own right, but they perform a number if important roles in the forest ecosystem, earning them the status of “keystone” species, species which play critical roles in the structure of their ecological community, thus affecting many other organisms belonging to different trophic levels in the food web.

Wood ants are believed to:

• Affect tree growth through their relationship with tree canopy aphids and through removal of insects that can cause pest outbreaks (caterpillars of moths such as the pine looper, Bupalus piniaria);
• Influence soil communities through excavation of their nests and by providing nutrients for new plant growth when a nest is abandoned;
• Provide food for a wide range of animals including green woodpecker (south of England), capercaille (Scottish Highlands) and badgers to name a few;
• Distribute the seeds of plants, including rarities such as small cow-wheat (Melampyrum sylvaticum), an endangered species; and
• Provide birds with a method of removing parasites – some birds are known to visit wood ant nests to be sprayed by formic acid which repels lice and mites

In addition to this, the thatched mounds of wood ants are home to a community of specialist invertebrates which are found no where else.

• The shining guest ant (Formicoxenus nitidulus): This tiny little ant is found only inside the nests of wood ants where it excavates its own nests inside deadwood. Living a mutualistic existence alongside the wood ants, the shining guest ant even “moves house” with the wood ants when their nests bud. Choosing to live only in the healthiest nests, once conditions deteriorate inside the mound the shining guest ant moves on with its brood to find a more suitable mound. Very little is known about the biology of this elusive little ant and it is a UKBAP Priority Species in the UK, being only found in a handful of wood ant nests in the Highlands of Scotland. If you are very lucky, you might see this tiny little ant, only a few millimetres long, moving across the surface of the thatch, its shiny cuticle makes it stand apart from the wood ants.
• Leaf beetles in the genus Clytra develop as larvae inside the nests of wood ants. The adult female rests on a branch overhanging a nest and drops her eggs onto the mound. The larvae protect themselves from the ants by living inside a hard case and can be seen crawling across the surface of the mound where they scavenge for food.
• A much larger beetle, the rose chafer Cetonia cupreae also lives in wood ants nests during the larval stage. The larvae feed on plant debris inside the nest.
• There are also a number of rove beetles in the family Staphylinidae which specialise in living in wood ant nests, but these are unwelcome guests, feeding on the brood of the ants. To avoid detection these beetles produce chemicals which disguise their presence and some go as far as producing sweet secretions from glands which the ants can’t resist and allow the beetle to roam about the nest unharmed.
• The woodlouse Platyarthrus hoffmannseggii is only found in ant nests. It is completely specialised to living in the dark chambers of the nest, having lost its eyes and pigmentation.