Lebia cruxminor (L., 1758)
Family: Carabidae

Lebia cruxminor (Figure 1) is a very attractive ground beetle with a specialised life history. It has a deserved reputation for rarity throughout its European range. The larva is known to feed as an ectoparasite on the pupae of the uncommon black leaf beetle Galeruca tanaceti (Figure 2). As the leaf beetle is comparatively uncommon it follows that Lebia which depends on it, is more so.

In brief

• In Northern Ireland recorded from fen pasture at Crom Castle, County Fermanagh. Overall, known from only three, very scattered, sites in Ireland

• Found in fen pasture and similar wet places in Ireland

• Usually appears in May to June

• It is rare and Northern Ireland is the stronghold for both the UK and Ireland

• Potential threats include drainage, nutrient enrichment and agricultural intensification.

• Feeds on the black leaf beetle Galeruca tanaceti, which also prefers wetter places in Ireland than in Britain.

Species description
Lebia and another ground beetle Panagaeus have similar elytral colours and patterns, but Lebia is smooth and shining whereas Panagaeus is dull and strongly hairy.

Life cycle

Similar species
Only one other beetle in Ireland comes close to the appearance of Lebia cruxminor and this is another ground beetle, Panagaeus cruxmajor. A photograph of Panagaeus can be found on HabitasOnline. Lebia and Panagaeus have similar elytral colours and patterns but Lebia is smooth and shining whereas Panagaeus is dull and strongly hairy.

How to see this species
This is a great rarity and unlikely to be seen by the casual observer. However, it may be looked for crawling on vegetation in semi-natural wet grasslands and the margins of fens in parts of County Fermanagh. Apart from the Crom Castle area, the highlands south of Lower Lough Erne are suggested as Galeruca has been observed there. It usually appears in May to June. Relevant access permissions should always be sought prior to visiting any sites.

Current status
Lebia cruxminor has been recorded three times in Ireland. Bullock (1914) took a specimen walking on a path in wet lake shore woods at Muckross near Killarney, County Kerry. Mackechnie Jarvis (1971) swept one from water meadows near Killaloe on Lough Derg.

In 1992 Keith Alexander, working as part of a National Trust Biological Survey Team, collected a single specimen off vegetation in fen meadow at Derrymacrow, Crom Castle, County Fermanagh (Alexander, 2003a). The association with wet meadowland is therefore fairly well established. We do not know with any certainty what its prey might be in these places, other than that G. tanaceti is favoured in Britain and Europe. This species is local and rare but has a wide range stretching across Eurasia from the British Isles to the R. Amur on Russia’s Pacific coast. It is rare in Britain (Luff, 1998), having been recorded recently only from small areas of east Cornwall and east Sussex. It has a deserved reputation for rarity throughout its European range.

In Ireland its habitat preferences, in so far as they are known, suggest an association with rich, natural, fen meadows or the flood zone of lakes. This differs from the situation in Britain where it has been recorded from dry calcareous grasslands (Alexander, 2003a). The difference may relate to its purported association with Galeruca tanaceti. The latter is recorded from dry, calcareous grasslands in Britain (Alexander, 2003b) but in Ireland most recent records relate to wet places, ranging from turlough margins (County Clare) to wet limestone grassland (County Fermanagh) or lakeshore flushes (County Mayo). There is one record for dry coastal sands, at Rossnowlagh, County Donegal.

Galeruca is polyphagous, that is, it can live on a variety of plants. In Britain, yarrow, thyme and knapweed are favoured (Prevett, 1953). All are common in Ireland but mainly in drier habitats. What its food plant in wet habitats might be is unknown but sneezewort, Achillea ptarmica, is common in the relevant areas of Fermanagh.

Why is this species a priority in Northern Ireland?

• It is rare with Northern Ireland being the stronghold for both the UK and Ireland.

It is characteristic of calcareous wet grassland, a threatened habitat in Northern Ireland.

Threats/Causes of decline
Unknown, but drainage, nutrient enrichment and agricultural intensification are all potential threats.

Conservation of this species

Current action

• A National Trust survey of the fen meadow at Derrymacrow, Crom Castle, County Fermanagh found this species in 1992

• Crom Castle is a National Trust property where the natural habitats are managed sympathetically

• Implementation of the Northern Ireland habitat action plans for Fens and Floodplain Grazing Marsh.

Proposed objectives/actions

• Maintain the viability of the population of this species

• Improve understanding of the status and requirements of this species

• Conduct a baseline survey of the Derrymacrow site, of similar sites in other parts of the Crom Estate and of further potential sites in the Lough Navar highlands where Galeruca tanaceti has been recorded. This should establish a ‘potential’ range for Lebia cruxminor using the occurrence of Galeruca as a baseline.

What you can do
If you encounter a beetle which suggests this species please note the locality from an Ordnance Survey map and report the details to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, Tel: 028 9039 5256, cedar.info [at] magni.org.uk or to roy.anderson [at] ntlworld.com.

Further information

Links
http://www.coleopterist.org.uk/

Ground Beetles of Ireland

Northern Ireland Habitat Action Plans

Literature

Text written by:
Dr Roy Anderson