Identification

The Scarce Blue-tailed Damselfly is one of a number of smaller damselflies found in Britain and has a fluttering flight. The males typically have a black abdomen with green or blue sides and a small patch of blue near the tip^1,2. Unfortunately they can easily be confused with the more common blue tailed damselfly (I. elegans) and careful examination is required to identify them accurately³. Closer inspection reveals that in the larger I. elegans, the blue patch at the end of the abdomen covers the top of segment eight where as in I. pumilio segments eight and nine are blue¹. When mature, females are greeny-brown on the thorax, but in the immature aurantiaca phase they are bright orange⁴. They do not have the blue tip to the abdomen. Males and females undergo age related change and consequently require care when being identified, as these changes are not always described in the literature³.

Status

I. pumilio is classed as nationally scarce in the British Red Data book of Insects. At the turn of the century it was believed to be almost extinct in the Britain⁵ although it may have been overlooked⁶. In recent times the species has shown some range expansion but despite this it still remains an endangered insect, reflecting the limited availability of suitable habitats².

Distribution

I. pumilio is predominantly a Mediterranean species which is distributed from western North Africa through Europe and the Middle East and across to west and central Siberia.

In Britain, I. pumilio is on the northerly limit of its range¹ and is most numerous in south-western counties of England and Wales⁶, being found from Hampshire, westwards to Cornwall and throughout Wales as far north as Anglesey¹. Additional sites are also scattered across Britain and Ireland² and isolated colonies exist in Gloucestershire, Wiltshire, Oxfordshire, Berkshire, Buckinghamshire and Bedfordshire¹. The southerly distribution of I. pumilio in Britain suggests that it is restricted by temperature⁷, especially as the species is known to colonise northwards and eastwards in favourable seasons^3,8. In recent years it has undergone an easterly expansion of its range in the British Isles⁹ and there may be further changes in the distribution as our climate warms.

Distribution map from the National Biodiversity Network Gateway website.

Ecology and Habitat Requirements

The habitat requirements for I. pumilio are not easy to pinpoint¹ and a clearer understanding of its natural history is essential if this insect is to be conserved. In Britain it can be found in a variety of natural wetlands including valley mires and floodlands¹⁰, as well as in artificial habitats³ and it appears to prefer sites with shallow water and little vegetation². These specific microhabitat requirements are scarce in Britain, undoubtedly contributing to the rarity of this species^7,11, but where they occur they are not usually exploited to the same extent by any other dragonfly species, thereby minimising competition⁸.

Typical natural wetland sites are usually small areas of shallow water, such as shallow bog pools or slow flowing water fed by seepages and flushes¹, that are often susceptible to drying out. Where these habitats are spring-fed they remain ice free in all but the coldest winters³ and the openness of the vegetation offers minimum shade probably helping to maintain the water temperature¹.

The most natural and undisturbed habitat conditions are found in Ireland, where I. pumilio favours shallow bog pools. It is believed that "these natural sites have provided the nucleus for dispersal into artificial water bodies such as mineral extraction sites and newly created ponds and ditches"³. Initially these man-made environments support little vegetation and provide an ideal habitat which this species is well adapted to exploit. Consequently, it is very likely that an increase in incidental habitat creation has contributed greatly to the expansion in range of this species1. However, colonies at artificial wetlands tend to be more transient¹⁰ and appear to undergo considerable fluctuations with changing habitat conditions. It appears that I. pumilio is associated with the early stages of plant succession^1,2. A common feature of most sites is a degree of habitat disturbance, which maintains bare substrate and openness of the vegetation².

The Scarce Blue-tailed Damselfly requires some emergent vegetation at breeding sites as the females oviposit into soft-stemmed aquatic plants, particularly soft grasses (Glyceria or Alopecurus), rushes (Juncus inflexus and J. articulatus) or spiked rushes (Eleocharis palustris)¹⁰ and occasionally Stoneworts (Chara spp)⁴. Females oviposit alone, settling on stems just above the water² where they commence egg laying by thrusting their ovipositor into the plant stem. The female often descends below the water's surface as as the eggs are laid³. The eggs hatch after 17 days and larvae can develop into adults within one year^1,2. "Rapid development and high adult mobility are essential attributes for this species which colonises temporary habitats"². The hatching process can be delayed in drought conditions and is stimulated by the return of normal water levels. This enables the species to survive periods of temporary drought¹².

The larvae live in, or on, silty muddy substrates, which support the early stages of plant succession¹. Newly emerged adults tend to shelter in the emergent vegetation, remaining close to the breeding site¹. Emergence appears to be influenced by temperature⁶ and usually lasts from late May until mid June. However, adults can be seen on the wing until early September (Figure 3).

Sites inhabited by I pumilio appear to have high water quality which can vary over a range of pH values. However, the species appears to favour mineral enriched water, particularly in slow flowing seepages, runnel and streams. In Wales mesotrophic dewponds and stock pools that are moderately base rich on mineral soils are frequented¹¹. I. pumilio can tolerate slightly brackish conditions¹³ and the static water in shallow ponds and lakes also provides a suitable habitat¹. These are more likely to be colonised when in the proximity of more suitable breeding habitat (Cham, pers. com).

Summary of main habitat requirements

The most important habitat requirements of I. pumilio are a combination of shallow, still or slow moving water, muddy, silty substrate and minimal vegetation. Despite the variety of water bodies inhabited by this species these microhabitat conditions are "remarkably similar at all sites"¹. Habitat disturbance can play a role in maintaining these conditions and preventing succession.

Current Threats

• Alteration of Hydrology - Drainage operations that divert water away from existing flushes and seepages cause habitat destruction and fragmentation.
  
  
• Changes in Created Water bodies - reworking of quarry sites is a threat, and inappropriate restoration of others, will lead to the drying-up of seepages and shallow pools.
  
  
• Succession - If left unmanaged, development of the vegetation and the encroachment of invasive plants will lead to the loss of colonies. Rapid growth of species such as Reedmace (Typha latifolia), which is quick to invade shallow water, can render sites unsuitable¹⁴.
  
  
• Lack of Knowledge - In general there are still large areas where our knowledge of this species is limited and a clear understanding of the ecology and biology of this species is important if it is to be conserved. Furthermore, the microhabitat requirements of I. pumilio are often overlooked by even experienced site managers.

Adapted from Cham et al, 1996¹

Management

General Guidelines

• Management of Temporary Wetlands - The decline in suitability of new habitats with succession means that it is important to clear and manage temporary wetlands on a rotational basis.
  
  
• Maintenance of Water Quality - Water quality and quantity should be maintained in spring-fed flushes and runnels³.
  
  
• Drainage operations - should not be undertaken that are likely to divert water away from occupied habitats. Similarly any planned abstractions should be appraised in relation to the likely effects on I. pumilio habitat.
  
  

Best Practice Guidelines

• Habitat disturbance is beneficial to I. pumilio and needs to be considered in site management. Grazing of vegetation and trampling in shallow water should be encouraged wherever possible as it maintains favourable conditions at some sites². However, over-grazing should be avoided as excreta can pollute the water and cause problems. Consequently, a careful balance must be reached. At quarry sites activities of motor vehicles have successfully prevented the encroachment of vegetation and have created water-filled wheel tracks which are often colonised. Habitat disturbance also helps to ensure the perpetuation of fine, bare substrates¹.
  
  
• Preventing Succession - The aquatic vegetation needs to be managed to maintain early successional stages as the larvae live in substrates that support early successional plants. Therefore vegetation should be removed on a regular basis and aggressive species such as Greater Reedmace, Typha latifolia and rushes restricted. These species not only choke aquatic habitats but also create shade and lower the temperature of the water³. Succession can be prevented by grazing but if this is not feasible, cutting is a suitable alternative.
  
  
• Maintenance of Emergent Vegetation - The maintenance of soft-stemmed grasses and rushes at an early stage of succession is advantageous for ovipositing females. The conservation of such habitat is also important for a range of other flora and fauna, which depend on similar specialised conditions. Positive management undertaken to maintain lagoons scraped bare of colonising vegetation would help to secure the future of I. pumilio populations¹⁴.
  
  
• Maintenance of Adjacent Vegetation - Areas of coarse, sheltered vegetation (long meadow grasses) should be maintained adjacent to emergence sites to provide safe areas in which newly-emerged adults can 'harden off'.

Habitat Restoration and Creation

• The creation of new pools and ponds on bare substrate suitable for colonisation should be attempted where possible. The limited availability of habitat for colonisation is an important reason why the insect remains threatened in many areas. In creating wetlands, areas of shallow water with flush or seepage areas should be provided to support this species.
  
  
• Translocation - I. pumilio is a dispersive species so translocation should not be necessary. However, in special circumstances it is feasible.
  
  

References

Management file updated on 27 January 2003