New Forest cicada (Cicadetta montana)
|Size||Body length: 16 - 27 mm|
Wingspan: 45 - 52 mm
Classified as Endangered in the UK, and protected under Schedule 5 of the Wildlife and Countryside Act (1981), as amended.
Cicadas are usually associated with hot countries, so some might find it unusual to learn that Britain has one listed as a native species. It is one of the UK's larger insects too, and a spectacular sight. The large wings are transparent and held 'roofwise' over the body when the insect is at rest. They extend beyond the abdomen when folded. The body is mostly dark slate-grey or black but the segments of the abdomen are ringed with gold. The legs are marked with orange.
This species is widely distributed geographically, being predominantly northern and Asiatic, but also found in the mountainous regions of southern Europe. In the UK, it is only known in recent times from the New Forest, Hampshire, with a few records from Surrey between 1864 and 1936.
The New Forest cicada is found in the habitat that lies between open grass or heathland and scrubby woodland. They require open sunny woodland rides and clearings bordered by scrub, or along woodland edges. These clearings need to be of sufficient size to remain open to full sunlight, whilst retaining a warm microclimate. South-facing, well drained slopes are ideal.
Adult cicadas are on the wing from late May to early July, and this adult phase of the insect's life lasts from two to four weeks. Both sexes feed on sap from twigs with their stout, needle-like proboscis.
After mating, females lay their eggs in the stems of herbaceous plants, small bushes and even bracken stems. The eggs hatch after 50 - 125 days, and the nymphs burrow into the soil. They stay underground for a period of six to ten years, feeding on the sap from the roots of various herbaceous plants and shrub. In their final spring, the nymphs construct a clay and leaf-litter turret on the surface of the soil above their burrows. This is thought to give the emerging insects an indication of the ambient air temperature.
Adult male cicadas sing from low bushes and vegetation, the song being a high-pitched ringing buzz lasting for many minutes. The song is produced by a membrane within the thorax of the insect, which clicks to-and-fro at a rapid rate, and is inaudible to most people above the age of 40 years. It can, however, be received by a modified bat-detector. Singing is only performed in still air in temperatures above 20° Celsius.
Although the New Forest cicada has probably never been common in this country, recent disappearances are linked to the loss of its favoured habitat. Most damaging is the constant year-round grazing pressure on the New Forest, resulting in a loss of the favoured scrub-edge habitat and the plants required for egg-laying and as food for the nymphs. The emergence turrets are prone to being destroyed by livestock trampling, which in turn leads to the nymphs being predated by ground beetles. An increase in bracken cover also lowers ground temperatures and shades out the ground where the nymphs develop.
The New Forest cicada is listed in the UK Biodiversity Action Plans (UK BAP) and is included in English Nature's Species Recovery Programme. The managers of the New Forest, Forest Enterprise, are working to create ideal habitat for this fascinating insect. Current research is aimed at discovering the exact details of its habitat requirements with the intention of creating the correct conditions in targeted areas of the Forest, and Bristol Zoo is beginning a captive breeding project, using stock from Belgium.
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- 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).
- Nymphs: stage of insect development, similar in appearance to the adult but sexually immature.
- Proboscis: a tubular protrusion from the anterior of an animal (e.g. the trunk of an elephant).
- 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.