Priority Species Workshops

One alien is a curiosity, two are an invasion - Ursula K. Le Guin

Background to project

In 2019 YWT on behalf of the Yorkshire Invasive Species Forum began a project in partnership with the Animal and Plant Health Agency (APHA) to deliver a number of workshops raising awareness of Priority Invasive Species to stakeholders and the wider community.  This formed a part of the 3 Year EU funded RAPIDLife project led by the Animal and Plant Health Agency, which is piloting an innovative approach to invasive species management. The project has a number of strands, including providing tailored training to stakeholders and the development of resources forming a larger toolkit to support wider INNS and biosecurity activities.

For information about Rapid see www.nonnativespecies.org/rapid


What are Priority Species?

We can view priority species as the next wave of invasive species. What is on the horizon and is at high risk of spreading to the UK? Which species are already here in small numbers but have the potential to grow in number and have larger impacts?

Priority species are:

– Highly likely to invade the UK or, if they are already present, highly likely to spread.

– Highly likely to cause significant damage to native wildlife and/or the economy.

Priority species are important as we have an opportunity to prevent these species from establishing and having larger impacts to the environment, society and economy if we act now. It is important that we can identify these species, report sightings early and put measures in place to control and eradicate new populations before they grow and establish.

Priority Species Profiles

There are currently 23 priority species listed for Great Britain. A spotlight on a few of these are listed below. For a full list of priority species please visit the Priority Species toolkit at www.nonnativespecies.org/rapid


Signal Crayfish

Pacifastacus leniusculu

Red undersides to the claw
White/Turquoise notch inbetween claws
Reddish Brown body

Native Range

North America – introduced to the UK in the 1970s, now widespread.


  • Carry Crayfish plague fungus which has and continues to cause huge declines in native White-Claw populations. In many UK rivers White-Claw crayfish have been wiped out.
  • More competitive, produce more young, eat more food, and more aggressive which reduces resources for native crayfish.
  • Contribute to erosion of river banks by very active burrowing. Small scale but due to numbers this can cause accumulated impacts on sediment input and stability of banks.
  • Predate heavily on native fish eggs and invertebrates.

Spiny-Cheek Crayfish

Orconectes limosus

Native Range

North America – Introduced to UK in 1995, only in a small number of locations but high risk of spreading further.


  • Carry crayfish plague fungus which has and continues to cause huge declines in Native White-Claw populations. In many UK Rivers White-Claw crayfish have been wiped out.
  • It is an omnivorous species, feeding on aquatic vegetation, fish eggs and invertebrates, and thus affecting biodiversity.
Abdomen has dark red bands
Tip of legs are orange
Prominent spines on cheek

Narrow-Clawed Crayfish

Astacus leptodactylus

Claws distinctively long, narrow and pale underneath
Leg joints often dark orange
Variable colour; can be brown, dark brown, green or blue

Native Range

Turkey, Ukraine and Southwestern Russia


  • Very competitive with other crayfish species, reduces resources available for other species.
  • Predates on inverts and fish eggs
  • Some signs of burrowing activity with potential to lead to increased bank destabilisation.


Carolina Fanwort

Cabomba caroliniana

Can appear tubular underwater
Leaves usually grow in opposite pairs, not in whorls
Fully submerged perennial plant – can grow up to 2 metres in length

Native Range

East North America and South America


  • Negatively impacts water quality especially during winter dieback, as nutrients released.
  • Clogs waterways, compared with native macrophytes caroliniana prevents light from reaching the water column, impacting on the whole aquatic ecosystem.
  • More competitive, produces more young, east more food, and more aggressive which reduces resources for native crayfish.
  • While caroliniana has high social value as an aquarium plant, in natural systems the plant can cause substantial nuisance to recreational users by impeding navigation, tangling fishing lines and wrapping motor propellers.


Myriophyllum aquaticum

Native Range

South America – established and spreading rapidly in southern England. Has been growing in the wild since 1960.


  • Carries Crayfish Plague Fungus which has and continues to cause huge declines in Native White-Claw populations. In many UK rivers White-Claw crayfish have been wiped out.
  • It is an omnivorous species, feeding on aquatic vegetation, fish eggs and invertebrates, and thus affecting biodiversity.

Crustaceans & bivalves


Emergent leaf spikes are pinnate (feathery)
Emergent spikes are anything up to 30cm long, with the trailing stems reaching anything up to 2 metres

Killer shrimp

Dikerogammarus villosus



Often has striped back but can appear uniform in colour also
Distinctive cones on tail
Larger than native shrimp. Size varies depending on age. Can grow to 30mm from tip of tail to tip of head, more commonly 10-20mm

Native Range

South-East Europe. Introduced to the UK in 2010.


  • It is a voracious predator which kills or simply bites off much more prey than it can consume
  • It readily consumes fish eggs and even attacks fish larvae
  • Due to its predatory activities it can significantly change natural food webs of invaded ecosystems and occupies high trophic levels comparable to fish

Quagga mussel

Dreissena rostriformis bugensis


Native Range

The Ponto-Caspian region of outh Eastern Europe. Introduced into the UK in 2014.


  • Full environmental impact still not fully understood. Possible impacts to transfer of resources in invaded ecosystems due to large scale filtering of nutrients.
  • Due to their ability to colonise hard surfaces, these mussels become a major fouling problem for raw water-dependent infrastructures, causing damage and increased operating expenses
Very similar to another invasive mussel, the Zebra Mussel, but can be separated on a few key points
Can show an obvious central stripe vs zigzag pattern on Zebra Mussel
Has an undulating seam and small basal groove vs straight seem and large basal groove on Zebra Mussel


Two workshops were conducted in 2020 in Yorkshire to introduce stakeholders to priority species. This included presentations detailing identification features, associated impacts and how to record and report species. The first workshop was held in January 2020 at Livingstone House, Leeds. The workshop was run in collaboration with Yorkshire Water and invited Yorkshire Water tenants to attend as these stakeholders are directly interacting with and managing activities within these aquatic environments which are a key pathway for the introduction of new INNS.

The second workshop was undertaken in March 2020 at Bradford & Bingley Sports Centre, working in collaboration with Aire Rivers Trust. This time, inviting a wider group of stakeholders who are interacting with the water environment.

Both workshops were a success with lots of interest from attendees sharing useful information on priority species and biosecurity along with methods of preventing the introduction of new species in the first place. We also had some interesting priority species drawings created by attendees which can now be appreciated by all!

Early Detection & Rapid Response

We can make informed predictions about the potential effects of invasive non-native species, but it is impossible to be certain what the effects will be (until it is too late). It is therefore important to deal with invasive non-natives as soon as possible, regardless of their perceived threat.

It is crucial that we identify new introductions of priority species as early as possible. This can help initiate a rapid response which can either contain, control or eradicate a new population before it becomes established and before it has chance to impact significantly on native wildlife.

How can I help?

Everyone can play their part in preventing new INNS from establishing.

1. Reporting new sightings

Report sightings by using iRecord (https://www.brc.ac.uk/irecord/ or the iRecord app) or by emailing alertnonnative@ceh.ac.uk

2. Biosecurity

A simple biosecurity kit can be made up of a hand brush, hoof pick and water bottle. Cleaning off shoes and equipment when a leaving a site can prevent the new establishment and spread of INNS.


The RAPID LIFE Priority Species Toolkit is available at www.nonnativespecies.org/rapid


This Includes:

– A full list of GB priority species

– ID Guides for all priority species

– Presentations about priority species and there impacts

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