Known by the scientific name of Dikerogammarus villosus, Killer shrimp are highly invasive species native to south-east Europe.

Although only found in a few populations across Britain, they can quickly dominate their freshwater habitats, killing invertebrates and small fish.

Killer shrimp are larger than their native freshwater counterparts and are distinguishable by cone shaped protrusions on their tails. They can survive in damp conditions for up to five days.

Native to the north-central and south-eastern US, the grey squirrel was first spotted in Britain in 1828.

Now common in all parts of Britain, the highly invasive grey has displaced native red squirrels from much of their former range.

Greys damage trees by gnawing young bark, causing commercial damage to forestry and nuisance to gardeners. They are also predators of birds' eggs and chicks.

Also known as "Japanese bamboo", knotweed is native to Japan, Taiwan and northern China. It can be found in Britain growing in urban areas such as waste land, railways and river banks.

Often growing into dense thickets, Japanese Knotweed was first introduced in the country in the 19th century as an ornamental plant. However, it has a detrimental impact on biodiversity as it competes with native flora and contributes to river bank erosion, increasing the likelihood of flooding.

The Country Land and Business Association estimates that it costs £1.5 billion a year to remove Japanese knotweed in Britain.

Common throughout Britain, rhododendron are thought to have come to the country from Spain. Distinguished by their large evergreen shrubs with leathery leaves and purple and pink flowers, rhododendron are still planted by gardeners today.

They are most common in acidic and peaty soils in woodland, river banks, gardens, and parks.

Native to south-west Europe and Asia, rhododendron were first introduced by gardeners in the late 18th century into parks and woodlands, where it was used for game cover.

Distinguishable by their small lobster-like appearence, the crayfish are easy to recognise. Threatening native white-clawed crayfish, the signal crayfish is much larger with red claws and a small turquoise or white blotch on the surface of its body.

The signal crayfish was first introduced on these shores for consumption in the late 1970s and 1980s but spread quickly across much of the UK.

As it is listed under schedule 9 of the Wildlife and Countryside Act 1981, it is an offence to release or to allow the escape of the species into the wild. In the UK it is an offence to keep any crayfish without a license, except in some parts of southern England.

A member of the cow-parsley family, a Giant Hogweed flower stems up to two and three metres high, with flowers up to 80cm in diameter.

Common in lowland parts of Britain, sap from Giant Hogweed sensitises human skin to ultra-violet light, leading to severe blisters. Affected skin can remain sensitive for several years.

A North American floating water plant, the Floating Pennywort is found mostly in the south-east of England and occasionally in the north-west of England and Wales.

It spreads rapidly and can grow up to 20cm per day, and may quickly dominate a body of water forming thick mats and impeding water flow and amenity use.

Pennywort was first naturalised in the UK in 1990 as a result of discarded plants from garden ponds.

The caterpillars of the Oak Processionary Moth are natives of mainland Europe. They were found breeding in the UK for the first time in 2006, on oak trees in Ealing and Richmond, in London.

The caterpillars feed on oak leaves and produce silken nests on the trunks of affected trees. They also have irritable hairs that carry a toxin which can be blown in the wind and cause serious irritation to the skin, eyes and bronchial tubes of humans and animals.

Native to China and north Vietnam, the Tree of Heaven was first recorded growing in the wild in the 1930s in Surrey.

Commonly found growing in urban areas and along London railway lines, Tree of Heaven was named as one of the top 100 most invasive species in Europe by Delivering Alien Invasive Species In Europe (DAISIE).

It grows by forming dense thickets with suppress other plant species and reportedly increases soil fertility.

Native to south-east Russia, Zebra Mussels reside in slow river water such as, canals, docks, lakes and can also be found water pipes and cooling systems.

They are marked by distinctive coloured stripes and threaten their ecology by smothering native species, rapidly filtering out nutrients from the water and clogging pipes.

The invasive Russian molluscs are commonly found across England, Ireland and at limited locations in Scotland and Wales.

A diving duck with a dumpy, short-necked shape and a longish tail, the duck's population in Britain has been reduced from 6,000 to 100.

First found in Britain in the 1950s, Ruddy ducks threaten native species through hybridisation and competition. The males of the species are chestnut-red with white cheeks and a swollen, bright blue bill. Females are brown with a dark cap and a horizontal dark bar across the cheek.