Invasive Species - Please be aware and report sightings

A number of invasive species can be found on WFFC waters, please report them if you come across them

Asian Hornets - Vespa Velutina

Asian hornets are now starting to spread across southern Britain and are a serious threat to natural insect species, not least pollinators in general and honey bees in particular. WFFC members should report any sightings and their locations ASAP to DEFRA (Department for Environment, Food & Rural Affairs), who will investigate and take action as necessary.

After first appearing in a coastal area of France, Asian hornets have spread widely across Europe. Parts of France are now believed to house approximately one nest per square kilometre and the sheer numbers have forced the closure of some late-summer food markets.
Asian hornets were first definitely identified in Britain in 2016 and sightings increased annually, albeit numbers were low. 2023, however, witnessed an exponential climb in sightings and nests, hence why action is being taken across the country now.
The initiatives are being led by beekeepers, who are particularly exposed to the threat. Honey bees have no defences against Asian hornets and it is believed that one Asian hornet can kill up to 25 honey bees per day.
In line with their potential routes of travel to Britain (air or shipping), Kent, especially coastal Kent, is the hotspot but there have been sightings much further afield. Two nests were destroyed in Devon in 2023, and one in Dorset.
Like most bees and wasps, Asian hornets are generally inactive or die during winter months. Queens (who mated in the autumn ready for the spring) survive the winter and go on the wing looking for suitable “primary nest” sites in early spring.
The potential population growth statistics are frightening. 1 queen can create a primary nest (generally around the size of a tennis ball) in the spring with up to 50 workers emerging. These will then seek to build a much bigger “secondary nest” which will grow and last until the autumn. These secondary nests have been known to house up to 30,000 individuals. The largest nests can produce up to 350 queens. These queens can attempt to repeat the whole process the following year.
Secondary nests can be broadly spherical structures up to around a metre in diameter. They are generally sited high up in deciduous trees but some are sited in hedgerows close to the ground - making them far more dangerous to humans and animals.
Asian hornets have similar broad diets to our native wasps and follow similar eating patterns. Earlier in the year they concentrate more on insects (although any form of meat can be consumed) but, as the need to feed larvae declines over the summer, they switch more to sugars. The latter brings them more into contact with humans.
Asian hornets are no more aggressive than our native hornets when encountered feeding. If a nest is disturbed, however, they become extremely aggressive and human fatalities have occurred in Europe. It is thus not recommended that anyone tries to interfere with any of these insects or their nests. If you find a nest, report to DEFRA.
The British Beekeepers Association have a website - www.bbka.org.uk/asian-hornet-incursion-map - and a link to a DEFRA app called Asian Hornet Watch - both useful for tracking and reporting sightings.
The Wildlife Trusts have a webpage showing the differences between the (much darker) Asian hornets and our native, European hornets. The page can be found at: www.wildlifetrusts.org/wildlife/how-identify/have-you-found-hornet

Signal Crayfish

WFFC has Signal crayfish on a number of its beats and you may often see remains on the bank where they have been eaten by otters

The White-clawed is the indigenous species of crayfish in the UK, it is dangerously vulnerable to the transmission of the deadly crayfish plague carried by the Signal crayfish. Apart from the disease issue, the Signals burrow into banks causing collapse, predate on invertebrates, fish eggs, fish and vegetation.

Signal Crayfish are fast breeders and they rapidly colonise and dominate new waters. They also grow faster, are more tolerant of a wider range of conditions and are more aggressive than the endangered White-clawed crayfish meaning they easily out-compete them.

There are restrictions on trapping and dispatching of Signal crayfish and this activity is regulated and licenced.

See the Angling Trust Signal Crayfish article for more details.

Himalayan Balsam

WFFC has Himalayan Balsam on a number of beats, Beat H just upstream of Iron bridge in particular.

Himalayan balsam (Impatiens glandulifera) has rapidly become one of the UK’s most invasive weed species, colonising river banks, waste ground and damp woodlands. It successfully competes with native plant species for space, light, nutrients and pollinators, and excludes other plant species, thereby reducing native biodiversity.

As an annual plant, Himalayan balsam dies back in the winter and, where the plant grows in river systems, can leave river banks bare of vegetation and liable to erosion. Dead plant material can also enter the river, increasing the risk of flooding.

Traditional control methods are currently inadequate in controlling Himalayan balsam in the UK. This is often because the plant grows in inaccessible areas or sites of high conservation value where chemical and/or manual control (weeding) is not an option.

See the CABI Invasive species article for more details

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