Narrow headed ant (Formica exsecta)
|Size||Queen length: 12 mm (2)|
Worker length: 10 mm (2)
Classified as Endangered in Great Britain (3).
The workers of this endangered ant can be distinguished from other wood ants by the characteristic deep notch on the back of the head (2). It is a medium-sized ant, red and dark brown in colour, and is aggressive (4). The wood ants are the largest of the British ants, all of which are reddish in colour and have a single segment forming the 'waist' (2). Reproductive females (queens) and males are larger than the workers, and have well-developed thoraxes and wings (which are shed from the body after mating). Males have obvious sex organs that protrude from the abdomen(2).
This ant is restricted to parts of southern England and the Scottish Highlands (4). In England, old records exist from the New Forest, Bournemouth, and parts of South Devon. There was also a population on the Isle of Wight, but the species has not been found there since 1913 (4). In Scotland it is known mainly from the mid Spey Valley, including the forests around Loch Morlich, Abernethy Forest and Carrbridge (4). It is currently only known in England from two sites in south Devon (5). It has undergone a serious decline, and it is thought that it may become extinct in England in the near future (4). This ant has a wide but patchy distribution in Europe (3). Elsewhere it if found from southern Spain reaching as far east as Mongolia and northern China, and from the Appenines to Arctic Scandinavia in the north (4).
Inhabits open lowland heathland or moorland in southern England and Caledonian pine forest in Scotland (4), where it is found in glades and at the forest edge (2). It may occasionally be found in rides and clearings in woodland, in scrub and by roads or paths (4).
This ant makes small nest mounds, which reach 25 cm in height and are around 30 cm in diameter. The core of the nest is either a tussock of grass or soil, covered with a 'thatch' of pieces of grass, heather and pine needles (4). The nests are located in sunny positions, which maximise the amount of sunlight falling on them (4). Coupled with the heat produced by the workers and the thatching (which helps to conserve heat) the nests are warmer than the surrounding soil (2). The nests usually have more than one queen and around 1000 workers. Although most recent records are of single, isolated nests, aggregations of 10-30 nests were once common, in which the workers of different nests interact without aggression (4). Usually, however the workers are extremely aggressive, and even attack larger wood ants, climbing onto the back of their opponent and decapitating them (4).
The workers tend aphids in order to obtain 'honeydew', a sweet substance excreted by the aphids. Invertebrates are also caught or scavenged and taken back to the colony (4). Winged males and females fly in July and August. The fertilised females may return to their nest, or establish a new colony (4).
The narrow headed ant has suffered as a result of habitat loss. In England heathland has been lost due to development, agriculture or forestry, or degraded due to unsuitable management, such as overgrazing, or through scrub invasion (3). In Scotland, native pine forests have been lost for similar reasons; a particular problem has been the intensive management of this habitat for game species (3). Other, more competitive species of ant may pose a threat; the southern wood ant (Formica rufa) is thought to over-run nests of the narrow headed ant (4). Fire, quarrying, and motorbike scrambling also pose threats to the fragile habitat, and the ant colonies (5).
Work to conserve the narrow headed ant has been funded by English Nature's Species Recovery Programme. The species has been identified as a priority for conservation under the UK Biodiversity Action Plan (UK BAP), and a Species Action Plan has been produced. The aims of this plan include the restoration of this ant to 10 populations in suitable locations before 2005 (3).
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).
- Rides: the footpaths and access tracks which run through and divide blocks of trees in woodland. Many rides contain a mixture of rich flora and structure, and provide different habitat conditions for a range of wildlife.
- 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.
- National Biodiversity Network Species Dictionary (January 2002) http://www.nhm.ac.uk/nbn/
- Skinner, G. (1998) British wood-ants. British Wildlife, 10 (1): 1-8.
- UKBAP (Jan 2002): http://www.ukbap.org.uk
- Falk, S. (1991) A review of the scarce and threatened bees, wasps and ants of Great Britain. Nature Conservancy Council, Peterborough.
- Pinchen, B.J. (2003) Pers. Comm.