You might barely notice it at your feet, but the wood ant is important. It is an “indicator species”, that is, their presence indicates healthy woodland.

There are several varieties in the UK.  The southern wood ant (Formica rufa) or horse ant is found mostly in the south of England, in Wales, and, less commonly, as far north as Cumbria and Northumberland. Scotland has the northern wood ant (Formica lugubris), the Scottish wood ant (Formica aquilonia) and the rare, narrow-headed ant (Formica exsecta).  The northern wood ant is also found just over the border in Cumbria and Northumberland.  They are found in both coniferous and broadleaf woodland, but like to be at woodland edges, along woodland rides or in clearings.  They like open woodland where their nest can benefit from the sun in the first warm days of spring (about now).  They also like a south-facing site to make the most of the warmth – they will even move a nest to be in the sunniest spot.  Only the Scottish wood ant is tolerant of denser, shadier woodland. 

It seems they prefer traditionally managed woodlands, particularly coppiced woods in the south, and well-maintained rides and clearing.  They will abandon a nest that has become overgrown or where the canopy has closed overhead. 

A wood ant nest is instantly recognisable – it looks like a roughly dome-shaped, untidy heap of leaves and twigs – and you will see trails of ants between the nest and their feeding trees.  Sometimes trails connect separate nests to make super colonies.  It’s better not to get too close or let your dog sniff – the worker ants are fairly aggressive and squirt formic acid if disturbed.  It smells like very powerful salt and vinegar crisps.

Their main food source is honeydew, a sugary substance produced by aphids, hence the trails to their favoured trees.  They also scavenge and will eat small invertebrates.

Why are these ants important?  In short, they help disperse seeds, they manage pests by preying on herbivorous insects that damage leaves, they contribute to nutrient recycling, their nests provide a habitat for a whole range of invertebrates that live specifically in wood ant nests, and they are a food source for various predators including the capercaillie.  Happily, on the whole the wood ant is doing pretty well and, with the exception of the narrow-headed wood ant, the UK Biodiversity Action Plan notes them as just needing “observation” – “Many southern wood ant sites are currently SSSIs, NNRs or are under sympathetic FC, RSPB, NT, local Wildlife Trust or private ownership.”  The Forestry Commission recognises them as a “keystone” species in the forest ecosystem and encourages woodland owners to treat them sympathetically. 

They seem pretty robust so long as the woodland is managed to keep their nest open to sunlight and they have a supply of aphid-bearing trees.  They do not do well with clear-felling which destroys nests and removes their food source, or dense conifer planting.  They also do not like repeated disturbance from people or livestock.  It is however, possible to manage felling sensitively, leaving some trees near the nest and being careful with heavy machinery.  The Forestry Commission can give advice.

See also:

Forestry Commission Information Note on “Forests & Wood Ants in Scotland”

http://www.forestry.gov.uk/pdf/fcin090.pdf/$FILE/fcin090.pdf

UK Biodiversity Action Plan Species Statement – Southern Wood Ant

http://www.ukbap.org.uk/ukplans.aspx?ID=311