Wiltshire and Swindon Biological Records Centre

Scarce Chaser - Libellula fulva

Scarce Chasers are, as its name implies, scarce, and the River Avon in Wiltshire is one of its strongholds. A colony can be found along a stretch of the Bristol Avon from Melksham, downstream past Bradford-on-Avon, and on into Somerset. 

Scarce Chaser, WSBRC/ Steve Covey

 

Habitat

The Scarce Chaser is primarily a riverine species preferring floodplains and watermeadows, and usually inhabits rivers with a slow to moderate flow. Occasionally they can be found in mature gravel pits such as at Cotswold Water Park. They prefer areas that have good water quality, which support submerged and floating plants, and emergent vegetation.

In June 2008 the Scarce Chaser was recorded for the first time away from its stronghold, and on the still waters of the Kennet and Avon Canal. Five Scarce Chasers, a mixture of males and females were found along the Caen Hill Locks. Find out more about this unusual record.

Description

The male and female are very different in appearance. The mature males have a pale blue pruinescence on the abdomen; the last three segments often turn black. Its eyes are also blue. Immature males look very similar to the female; they are both vivid orange in colour, with black triangular shaped marks on the base of each abdominal segment and dark bases to the wings.

The mature male is often confused with either the Black-tailed Skimmer or the Broad Bodied Chaser as both have blue abdomens. The blue eyes help to distinguish it.

Biology

They are active May to July, with the peak time being June, although they can sometimes be seen on the wing until early August.

Once mating has taken place the female oviposits in areas of slow flowing open water, often close to the bank or above leaves of an aquatic plant lying in the water. She is guarded by the male who hovers nearby to ward off intruders. The eggs then sink to the bottom and become attached to the mud of the riverbed. Once hatched, the larvae may take up to two years to fully develop and emerge in May.

Dense vegetation is important in all stages of the Scarce Chasers life. It provides a niche for developing larvae in the roots; it also offers shelter and emerging, basking and resting sites for the adults. Adults bask on top of the vegetation and can be found in a few numbers where there is scrub in close proximity to the river. Males are often seen flying along the waters edge, not over open water. Females are most often seen flying away from the river.

Threats

Scarce Chaser populations, although rare, seem to be stable. They can be threatened by bad river management, pollution and changing water levels.

Conservation

Due to its scarcity in Britain, and loss of its specific ideal habitat, the Scarce Chaser is listed under category 3 (scarce) in the British Red Data Book on Insects.