Local Non-Native Species Survey


This is an ongoing local citizen science initiative to determine whether, and to what extent, non-native and invasive species are present in the Upper Nar area.  Monitoring biodiversity, and particularly invasive species, is more important than ever with climate change affecting local ecosystems.  Potentially, some invasive species could affect soil fertility or pollination and so have an impact on food production.  Gathering information about where invasive species are found and in what quantity is crucial for planning strategies for their control.

Scope of the Survey

The survey is focussed on the Upper Nar area and on a limited number of named species, though you can submit other non-native species sightings.  For the named species, please report any sighting, whether in a garden or not.  If you report other problem non-native plant species, such as Russian vine, only do so if it's outside of a garden.  The majority of garden plants are non-native; it's the escapees that need monitoring.

Further down this page, there is more about each of the named species,  If you have seen one of these species in the Upper Nar area, please identify the location using the What3words mapping system (help page) and then fill in the UNG Record a Sighting form*.

At the bottom of this page there is a map showing results so far.

The survey is organised by Jeff and results will be shared with the national UK Biological Records Centre (BRC) and regional Norfolk Biodiversity Initiative (NBIS) and Norfolk Non-Native Species Initiative (NNNSI).

The focus invasive species are:

Invasive Plants

There is comprehensive legislation about invasive plant species that lists those species where it is an offence to "import, keep, breed, transport, sell, grow, cultivate or permit to reproduce".  

Of these plants, the ones of particular concern are:

Japanese knotweed

Japanese knotweed (Reynoutria japonica, syn. Fallopia japonica) was widely planted as an ornamental during the Victorian era, and having escaped from gardens, has now spread to almost every part of the UK. Japanese knotweed damages native ecosystems as the species outcompetes other plants and currently in the UK, it has no natural predators.  It causes significant economic burdens; clearing the London Olympic site is estimated to have cost £70 million (source RHS).  Mortgage lenders are very cautious about Japanese knotweed (here's why: BBC video) and allowing it to spread can result in prosecution (eg 2019 case).  Although Japanese knotweed does not produce seed in the UK; all plants are clones of a single female specimen collected in 1850, as little as half a gram of stem or rhizome is sufficient to produce a new plant.

Local Occurrence

To date, although Japanese knotweed has been recorded in Fakenham and Castle Acre, there have been no reports in the Upper Nar area shown in the map below (UNG catchment area).  Please keep an eye out for knotweed in this area and report any you see.

Reference information:  Gov.uk information page

Giant Hogweed

☣️Contact with any part of this plant must be avoided. Even minute amounts of sap can cause blistering of the skin with exposure to sunlight (eg news article).

Inflammation and blistering can begin in as little as 15 minutes after contact with sap, and dangerous sensitivity to sunlight can last for several days. 

⚠️ Protective clothing, including eye protection, should be worn when handling giant hogweed* .

Introduced as an ornamental, giant hogweed (Heracleum mantegazzianum) was first recorded growing wild in the UK in the late 19th century.  

Fully grown giant hogweed is a huge plant; typically it grows to heights of 2 to 5 m (6'7" to 16'5"). The leaves, which are usually incised and deeply lobed can be between 1–1.5 m (3'3"–5'11") wide, The plant generally has a stout, bright green stem, up to 10cm (4") diameter with dark purple splotches and prominent coarse white hairs, especially at the base of the leaf stalk.

Giant hogweed can however be very variable in  appearance; some botanists consider Heracleum mantegazzianum to be a group of perhaps five related species.

Giant hogweed spreads by seeds, mainly through wind dispersal and via water courses.  It is often found next to rivers.

Local Occurrence

Giant Hogweed has been recorded next to the River Nar near to West Lexham.

Giant hogweed (Heracleum mantegazzianum)
Image credit: GerardM CC
* Sap of the much smaller native hogweed can also cause some degree of photodermatitis.

Himalayan balsam

Himalayan balsam (Impatiens glandulifera) is another escaped ornamental, originally introduced from Asia in the 19th century.  A relative of the 'busy Lizzie', it is a fast growing annual that reaches 2m to 3m in height and, like Japanese knotweed, can outcompete native plants.

It is frequently found on the banks of waterways, where it can form continuous stands. It also thrives in damp woodland.  

Reproduction is by seed, which is distributed by the explosive seed pods; the pods can jettison seed up to 7m. Seeds are also carried by watercourses, and by people picking seed heads.

Local Occurrence

Himalayan balsam has been recorded in Narborough to the West and  Beetley to the East.  There has been none formally recorded in the UNG catchment area to date.

The three preceding species, Japanese knotweed, giant hogweed and Himalayan balsam, were all introduced by the Victorians during the 19th century and promoted at the time as having '...the virtues of "herculean proportions" and "splendid invasiveness" which meant that ordinary people could buy them for the cost of a packet of seeds to rival the expensive orchids grown in the greenhouses of the rich.' (source)

Rhododendron ponticum

A large evergreen shrub with leathery leaves, attractive purple flowers and solid stems forming a trunk when mature.  Rhododendron ponticum spreads by layering, where branches touch the ground, and by seeds which are carried long distances by the wind. Each flower head can produce between three thousand and seven thousand seeds.

It was originally introduced by Conrad Loddiges in 1763 as a garden ornamental, but was also extensively planted in Victorian hunting estates to provide shelter for game species.

It is an acid loving (ericaceous) plant that often grows in ecologically sensitive habitats, such as heath and broad-leaved woodland where it can form large stands which create dense shade. Many native species in the ground layer of plants are shaded out of existence, and many trees species cannot regenerate under a rhododendron canopy.

Local Occurrence

None recorded in the UNG catchment area to date.

New Zealand Pygmyweed

Crassula helmsii

Introduced in 1911 as an oxygenating plant for ponds.  In the last fifty years it has become a significant problem.  It can form dense mats in slow moving water and can block drainage channels causing flooding.  It out-competes other aquatic plant species.

Local Occurrence

It has been found in one pond on Litcham Common and at least one garden pond nearby.  Please report any other observations so that we can build up a picture of how extensively Crassula helmsii is distributed in the Upper Nar area.

New Zealand Pygmyweed(Crassula helmsii)Image credit: UK NNSS

Invasive Animals

As with plants, there is legislation about invasive animal species which lists those species where it is an offence to keep them.  

This survey is focussed on the following animals:

Asian Hornet

Update September 2023

There has been a significant rise in the sightings of Asian hornets during 2023 compared to previous years, with fifteen nests found in the south (Kent, Dorset, East Sussex and Devon).  There have still been no sightings in Norfolk to date, but we need to be vigilant.  News Article and List of Sightings (gov.uk)


An invasive predator of honey bees and other insects.   

⚠️ Do not under any circumstances disturb or provoke an active hornets’ nest.

The Asian hornet (Vespa velutina) is native to eastern Asia. It was accidentally introduced into Europe, probably in a consignment of pottery from China. It was confirmed in south west France in 2004 and quickly spread across France, and is now found in much of Europe as well as the Channel Islands. The Asian hornet preys predominantly on honey bees. Additionally, it poses a health risk to those who have allergies to hornet or wasp stings. 

The Asian hornet was discovered in the UK for the first time in 2016 by a beekeeper in Gloucestershire. 

In the past few years there have been further sightings in the South and West, but none formally recorded yet in Norfolk.

See the APHA blog for more about the Asian hornet.

The Asian hornet is active mainly between April and November.

If you see/photograph an Asian hornet, please report it through this website's Report a Sighting form.  You might also want to report via the Asian Hornet Watch app, available for iPhone and Android phones.

Local Occurrence

None recorded in the UNG catchment area to date.

Other Hornets

Our native European hornet can be distinguished by its abdomen which is generally yellower, more like a wasp's.  They have brown, not yellow, feet.

Also in the news sometimes is the Asian Giant Hornet, or 'murder hornet', though this has never been sighted in the UK to date.

Asian hornet (Vespa velutina). Note the yellow feet.

Video credit: APHA
Picture of a native hornet

Native European hornet (Vespa crabro). Note the brown feet.

Image credit: Niek Willems 

Marsh Frog 

The Marsh frog (Pelophylax ridibundus) is the largest of three green frog species found in the UK, and is an invasive non-native.  The other green frog species are the non-native edible frog and the native pool frog, which is very rare.

Marsh frogs were introduced into Kent in 1935 from Hungary and are now found predominantly in south-east England and Norfolk. Although the marsh frog mainly eats invertebrates, it can eat fish, young birds and other amphibians.

Marsh frogs are around 50% bigger than a common frog, with a rounded snout and warty skin that varies from olive to bright green, with irregular dark blotches. There is sometimes a bright green or yellow line running down the centre of the back. Their underside is creamy white. They also have a ridge running along each side of the body, starting just behind the eye. Marsh frogs don't have the dark 'mask' behind the eye, which is seen on common frogs.  They have two vocal sacs which are grey.  

Marsh frogs can often be found by the male's 'laughing' call (audio links on this page).

Their tadpoles grow considerably larger than those of native frogs (see the photo below).

Local Occurrence

Marsh frogs have been reported in mid-Norfolk, though there have been no reports to date in the Upper Nar area.

Marsh Frog ♂ Call Recordings

Recording #1 by Llivermore. CC.
Recording #2 by Dimitǎr Boevski. CC.
Marsh Frog (Pelophylax ridibundus).  An individual with a line running down the centre of the back.Image credit: Calimo 
Marsh frog showing characteristic grey vocal sacsImage credit: Peter Trimming
Marsh frog tadpole Image credit: Вальдимар

Lily Beetle

Lilioceris lilii, sometimes called red lily beetle or scarlet lily beetle, feeds on lily, cardiocrinum and fritillary plants. They eat the leaves, stem, buds, and flowers.

The beetles overwinter as adults in soil or leaf litter which may be some way from the host plants. Beetles can fly to find new hosts in the spring, which they can locate by smell.

The beetles begin emerging on sunny days in late March and April when they seek out the foliage of host plants.

They are very easy to spot as they are bright scarlet and about 8mm long.

Local Occurrence

Recorded in Litcham and East Bilney.

Rosemary beetles

These pretty metallic looking beetles are 6mm to 8mm long and affect not just rosemary plants, but also the related species, lavender, sage and thyme.

An invasive insect that first appeared in the UK in 1994, they have spread through the southern counties and are increasingly found further north.

Adult beetles are usually first seen in late spring, although they remain largely stationary on plants until later in the summer when they start to breed.

There are currently no natural enemies commercially available to control rosemary beetle.

Local Occurrence

Recorded in Beeston.

Non-Native Flatworms

Britain has four native species of land dwelling flatworms and now, over fifteen non-native species.  All flatworms are predators, and some of these invasive flatworms kill and consume our native earthworms.  This may ultimately have a significant effect on soil structure and fertility, for which earthworms are so important. 

They generally live in damp soil and can often be found under stones or logs.

The flatworms of most concern are:

Although in parts of the UK some of these flatworms are widespread, East Anglia has had few reports. This could be because invasive flatworms haven't established here, or it may be a lack of reporting?

If you find a flatworm and would like help in identifying it, contact Jeff.

Local Occurrence

None recorded in the UNG catchment area to date.

Video of an Obama flatworm overpowering and consuming an earthworm.  Best viewed full-screen and not last thing at night.

Video credit: Iñaki Rojo 


The Obama flatworm derives its name from Brazil's indigenous Tupi language; Oba ma means leaf animal. Nothing to do with presidents.


Flatworms can be mistaken for slugs, but can be distinguished by their lack of tentacles and their smooth unsegmented skin surface.


Flatworms can't be killed by chopping them in half - it just creates two flatworms.

New Zealand flatworm
(Arthurdendyus triangulatus)

Image credit: S.Rae

Australian flatworm
(Australoplana sanguinea)

Image credit: Jon Sullivan 

Kontikia flatworm
(Kontikia andersoni

Image credit: Mark Telfer

Obama flatworm (Obama nungara)

Image credit: Pierre Gros

Obama flatworm showing underside

Image credit: Pierre Gros

Obama flatworm eating an earthworm

Image credit: Pierre Gros

Brown Marmorated Stink Bug

Since 2018, the Brown Marmorated Stink Bug (BMSB) has been found a few times in Southern Britain, including the RHS garden at Wisley in 2021.  These individuals don't yet seem to have formed breeding populations, but surveillance is necessary.  More information at the Natural History Museum.

Local Occurrence

None recorded in Norfolk to date.

Picture of a stinkbug

Brown marmorated stink bug (Halyomorpha halys)

Image credit: Tim Haye/CABI

Local Species Survey: Results So Far

The non-native red-legged partridge and ring-necked pheasant are excluded as they are bred and released in large numbers for shooting (ca. 60 million birds in the UK RSPB).

You might also be interested in the National Biodiversity Network Trust map of all species recorded in the Upper Nar area.

* Only record species where it is entirely safe and legal to do so.  Do not take personal risks or trespass on private land for the sake of this survey.  The Upper Nar Gardeners group does not accept any liability or responsibility for the wellbeing of surveyors.