Scarce Yellow Sally

Fast Facts

Latin name: Isogenus nubecula

Notable feature: Adults are fully winged and have two long tails (known as cerci)

Conservation Status: Critically Endangered

Where in the UK: Only found along parts of the main channel of the River Dee in Flintshire, Wales.

Scarce Yellow Sally Stonefly (Isogenus nubecula) © Mike Hammett


The Scarce Yellow Sally (Isogenus nubecula) is a Critically Endangered, native stonefly which is only found along parts of the main channel of the River Dee in Flintshire, Wales.  One of five species of Perlodidae (stonefly family) known from the UK; this species is typically found in large stony lowland rivers.

Adults have two long tails (known as cerci), and both the female and male are fully winged; they are grey in colour with a pale stripe on the thorax.

The larvae (also called nymphs) are dark with yellowish markings and are covered with pale clothing hairs.

Larvae can be found by kick sampling – disturbing an area of riverbed and collecting the dislodged invertebrates in a net.  Adults can be found by examining trees and other vegetation or by turning stones at the side of the river.

The Scarce Yellow Sally is also known as the Rare Medium Stonefly.

    • Size: Females are typically 15-20mm long, while males are slightly shorter at 14-19mm.  Larvae are 14-20mm long.
    • Life span: Adults can live between 30-40 days, whilst larvae can live approximately 1 year.
    • Diet: Scarce Yellow Sally larvae are predatory, feeding mainly on mayfly and non-biting midge larvae, although they may also eat some vegetation. Scarce Yellow Sally adults are thought not to feed, though they do drink water.
    • Reproduction: Most stoneflies lay eggs in masses and the female will either lay her eggs while dipping her abdomen into water or drop them when flying above.
    • When to see:  Adults are reported as being on the wing between March and April however there are sources from Europe that suggest the flight period extends later until June.
    • Population Trend: The Scarce Yellow Sally is declining.
    • Threats:  Water pollution is a significant threat to this species. Water quality in the River Dee is generally good, however pollution incidents, particularly those that occur above Bangor-on-Dee, may be detrimental to the survival of this species. This species may also be impacted by climate change with predicted rise in water temperatures. This species may also be affected by disturbance of habitat by livestock and the adults may be affected light pollution.
    • Fun Fact: The Scarce Yellow Sally was thought to be extinct in Britain, having last been recorded in 1995, but a small population was found on the River Dee in Wales in 2017.

How you can help: 

Buglife is working to increase awareness of invertebrates and the Scarce Yellow Sally through specific projects, such as our Scarce Yellow Sally project which is a part of the larger Natur am Byth! partnership programme, and campaigns which have highlighted the damage caused to our freshwater invertebrates through the actions of humans, but we need your help!

Join a recording scheme and log your finds – more information on how to do this can be found on the Riverfly Recording Scheme web pages.

Do remember that we rely on donations to continue our work.  If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a DonationBecoming a Member or maybe even making a purchase in our shop.  For more ideas on how to support our work find out how to Get Involved.  Thank you 🕷