Southern wood ant  (Formica rufa)

Classified as Lower Risk-near threatened (LR/nt) in the IUCN Red List (3) and classified in Great Britain as Local (4).

The southern wood ant can generally be distinguished from similar wood ants by the fact that it lacks a fringe of hairs on the eyes and the rear margin of the head (5). The wood ants are the largest of the British ants; and all are generally reddish in colour (5). In contrast to workers, reproductive females (queens) and males have well-developed thoraxes and wings that separate from the body after mating. Furthermore, males have obvious sex organs that protrude from the abdomen(5).

In the UK, the southern wood ant is a local species occurring predominantly in southern England and Wales. Although it seems to be increasing in numbers in the south of England, the range is shrinking southwards (4). The species has become locally extinct in parts of the former range in the north and east of England, the Midlands and north Wales. Outside of the UK, this species is found throughout the Palaearctic(4).

Nests are found in open woodland in glades or rides or at the woodland edge (4).

The mound-nests of this species are large, isolated and thatched (5), and a single colony can consist of more than 250,000 individual workers that aggressively defend the territory(5). Wood ants are carnivorous, and workers carry a wide variety of prey back to the nest along trails that extend throughout the territory (5). Studies of the southern wood ant have shown that around 60,000 food items are taken to the nest each day (5). The workers also tend aphids for the sugary 'honeydew' that they exude from the anus; the aphids gain protection from predators in return for this service (5). Southern wood ant workers have been observed climbing up 30-metre tall Scots pine trees (Pinus sylvestris) in order to obtain this honeydew (5), and it has been shown that every season, workers take a massive quarter of a tonne of honeydew back into the colony (5).

At the beginning of spring each year, unfertilised eggs are produced, and these develop into males. Other eggs that are produced at this time and are fed more become queens, while others develop as workers. During June, usually on a warm humid day, huge numbers of winged reproductive males and queens leave the nest en masse and engage in a mating flight. After mating, the male soon dies; the queen sheds her wings, and searches for a suitable location to establish a new nest (5).

Although the reasons for the decline are not fully understood (5), it is thought that loss of woodland habitat and unsuitable management practices leading to overgrowth of sunny areas, as well as disturbance by humans and livestock may be involved (4).

The southern wood ant is a UK Biodiversity Action Plan (UK BAP) priority species, the Species Action Plan aims to maintain a network of populations throughout the UK range. A number of colonies occur within National Nature Reserves (NNRs), and Sites of Special Scientific Interest (SSSIs) and so will be afforded a degree of protection (4).

Information supplied and authenticated by Bryan Pinchen (independent ecologist).

• Abdomen: in arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree. In crustacea (e.g. crabs) the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
• Palaearctic region: the region that includes Europe, the part of Asia to the north of the Himalyan-Tibetan barrier, North Africa and most of Arabia.
• Territory: area occupied and defended by an animal, a pair of animals or a colony.
• Thorax: part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.

1. UNEP-WCMC (Jan 2002): http://quin.unep-wcmc.org/
2. Skinner, G. (1987) Ants of the British Isles. Shire Natural History, Shire Publications Ltd, Aylesbury.
3. IUCN Redlist (Jan 2002): http://www.redlist.org/
4. UK BAP (Jan 2002): http://www.ukbap.org.uk
5. Skinner, G. (1998) British wood-ants. British Wildlife, 10 (1): 1-8.