Glow Worm

Durham Priority Species
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Glow Worm Action Plan

Priority Species: Glow Worm

Priorities

  1. Improved knowledge on the distribution, local habitat requirements and autecology of glow worms
  2. Protection of all known and historic glow worm sites
  3. Improve connectivity of semi-natural habitats near and adjacent to glow worm colonies

Targets
Vision Statement:  For known sites to be protected and to have more complete distribution data, and a better understanding of their habitat requirements

Target Type Unit Value
1. To maintain the population of glow worm on known sites. maintain glowing females 40
2. To expand the current known range of glow worm through increased survey effort. expand occupied tetrads 10

The glow worm is a small beetle, up to 25mm long in length and sexually dimorphic.

Only the wingless female glows strongly, to attract the flying males. Each individual female has an adult glowing life of only a few weeks until she mates, since she dies soon after laying her eggs.

After a few weeks the eggs hatch into larvae, and they remain as larvae for one or two further summers, feeding on small snails which they apparently paralyse before sucking them empty.

Though they favour chalky or limestone areas, they have been reported in the past from many areas of Great Britain. They are found in gardens, hedgerows or railway embankments, but also on cliffs, woodland rides and heathland. Although more common in the south of England, glow worms are recorded from much of the UK.

Because female glow worms are flightless, colonies do not migrate fast, and the species has difficulties colonising new sites, particularly with increasing fragmentation of suitable habitats.

It is thought that the glow worm is declining throughout its range.

Surveying

Finding glow worms on known sites is relatively easy. After dark on warm summer evenings from the end of May onwards females are clearly visible as a small green glow – rather like a small LED – in open areas of grassy vegetation.

The difficulty in mapping their distribution is in knowing which other sites to survey, since we are not certain of their habitat requirements.

Also the two- or maybe even three-year gap between a mating and the subsequent appearance of an adult means you may find plenty on a site one year, yet few or none at all the next. Therefore sites where they seem to have died out or where they have not been recorded can’t be written off on the basis of a single night’s search.

Local status

In Durham there are only a few currently known sites for glow worm, including Thrislington National Nature Reserve, Beacon Hill on the Durham Coast (magnesian limestone sites) and Hamsterley Forest.  At Thrislington, a former stronghold for the beetle, numbers have declined dramatically in recent years.

Other historic records include Muggleswick, Annfield Plain and Trimdon Grange.

Threats

  • Fragmentation of habitat will limit colony expansion or migration and limit the ability of glow worms to survive local extinctions.
  • Lack of knowledge of distribution and lack of protection for sites will allow inadvertent destruction of colonies.
  • Lack of knowledge of habitat requirements means that it is difficult to avoid inappropriate management.
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