SPECIES MANAGEMENT SHEET

(Spiriverpa lunulata)

Northern silver-stiletto

The Northern silver-stiletto fly is a rare species

strongly associated with exposed river shingle

and sandy sediment deposits. The adults

have an elongated silvery body with silvery-

white hairs on the abdomen and face. The

larvae are predators of insect larvae in sandy

flood deposits. Adults feed on nectar and

pollen from flowers and can be found basking

in sunny spots on sandy banks. Hovering

swarms of males can occasionally be

encountered. This is a UK Biological Action

Plan priority species, a Red Data Book

species, it is on the Scottish Biodiversity List,

and is a priority species in the Cairngorms

Nature Action Plan.

Life cycle

Adults have been recorded from April through to

September, with a peak from mid to late June.

Swarms of hovering males may form on riverbanks

and females enter the swarm to mate. Adults have

been reared from larvae found in sandy river

sediments and are carnivorous, likely hunting

various insect larvae and earthworms.

Distribution map

This is a northern European species with records from

the north and west of Britain, Norway, Sweden and

Finland. The majority of the British population is found

in the Central Scottish Highlands around the Spey

Valley and Easter Ross, but there

are records from the Scottish

Borders, Dumfries & Galloway,

Perthshire, Stirlingshire and

some western counties of

England and Wales.

Habitat

This species is associated with

open areas of exposed sediment

along sandy or stony rivers,

upland streams and around

sandy floodplain deposits. Sandy

river banks with sparse vegetation that are unshaded by

trees and receive regular deposits of loose sediment from

floods or spate events are favoured by adults. The exact

requirements of the larvae are poorly known, but they

appear to need an abundance of exposed sandy deposits.

Dark green post-1980, light green pre-1980

Left: Northern silver-stiletto fly (Spiriverpa lunulata) Right: Exposed riverine shingle next to River Tay at Kercock (typical habitat)

Reasons for decline

This species may be threatened by river

‘improvement’ and flood prevention schemes that

alter sediment deposition, sand and gravel

extraction, afforestation, excessive trampling and

agricultural pollution.

Habitat management

Measures to help conserve the Northern silver-

stiletto fly (that will also benefit a range of other

rare species) include:

Prevent the removal of gravel and sandy deposits

and maintain exposed areas of sand and shingle

banks in an undisturbed state.

Avoid changes to river management that would

prevent regular deposition and movement of

sediment by spate and flood events.

Prevent the encroachment of trees and scrub

close to river banks that would shade exposed

areas of sand used for breeding.

Avoid the build-up of herbaceous vegetation on

exposed riverine sediments that will cover

breeding habitat.

Avoid the use of agricultural chemicals and

pesticides near watercourses.

References:

This sheet can be accessed on the web at www.buglife.org.uk

Stubbs, A.E. and Drake, M. (2001) British Soldierflies and their Allies, BENHS.

Oldroyd, H. (1969) Diptera, Brachycera, Section (a) – Tabanoidea and Asiloidea. Handbooks for the Identification of British Insects, 9 (4): 1-132

Drake, C. M. , Godfrey, A.G., Hewitt, S. and Parker, J. (2007) Fly assemblages of Exposed Riverine Sediment.– final Report. Buglife publication.

Buglife—The Invertebrate Conservation Trust, Balallan House, 24 Allan Park, Stirling, FK8 2QG

Buglife—The Invertebrate Conservation Trust is a company limited by guarantee.

Registered in England at Bug House, Ham Lane, Orton Waterville, Peterborough, PE2 5UU. Company no. 4132695,

Registered charity no, 1092293, Scottish charity no. SC040004

Photographs of Spiriverpa lunulata © Roger Key; Habitat photographs © Steve Hewitt

Acknowledgements: Steve Hewitt and Martin Drake, Diptera experts

www.buglife.org.uk Tel: 01786 447 504 @buzz_dont_tweet

Survey methodology

Surveying should ideally take place between May—

late July, roughly between 10am—4pm during dry and

sunny weather conditions.

Sweep netting river bank areas deemed suitable to

support the adult fly should be carried out. Searching

on the bare sand banks should also be checked for

resting adults.

Care is needed to ensure that a similar stiletto fly

Acrosathe annulata, also found in the Spey Valley, is

discounted (this specimen is almost identical to

Spiriverpa lunulata in the field). Voucher specimens

will need to be collected and identified to confirm the

presence of the Northern silver stiletto fly.

A sufficiently experienced surveyor should be

employed to conduct the survey.

Left: Exposed riverine shingle habitat next to River Feshie Speyside; Right: Northern sllver-stiletto (Spiriverpa lunulata)