Invasive Species

Invasive Species

Asian Hornet

Invasive species on Alderney

'Alien’, ‘non-native’ and ‘introduced’ are all terms that refer to species that have been introduced to an area outside of their natural range, often due to human activity. These introductions are rising sharply, due to increased trade, transport and travel. When an introduced species is seen to be causing damage to the environment, the economy or human health, they become known as invasive species.

Invasive species may be bigger, faster growing or more aggressive than native species. They may also have fewer natural predators to control numbers. Native species are often unable to compete and quickly the invasive species can take over. Thus, the survival of vulnerable species is put in jeopardy, and damage is done to sensitive ecosystems. The impact of invasive species is now considered to be one of the greatest threats to global biodiversity.

Invasive species do not only cause damage to the environment, but also to the economy, our health and lifestyles. In Britain alone, invasive species cost around £1.7 billion a year; and the problem only escalates as the species spread. In the UK some of the worst invasive species include Japanese Knotweed, Signal Crayfish and Grey Squirrels. 

Three of the most harmful invasives on Alderney are listed below.

Asian hornet compared with wasp

© Andy Marquis

Asian Hornet

The Asian hornet (Vespa mandarinia) is an aggressive predator of many types of insect but on average 30% of its diet is made up of honeybees. The Asian hornet is therefore a major threat to our biodiversity, pollinating insects, and beekeeping activities. It was first found in Alderney in 2017 and the States of Alderney are encouraging anyone who thinks they have seen an Asian hornet or found an Asian hornet nest to report it to the State’s Agricultural Team   The AWT support the states team in their constant search for nests and often work in conjunction to help access and destroy less accessible ones.

What do Asian hornets look like? - Asian hornets have a distinctive velvety black/dark brown thorax. The abdomen is also black/brown with the abdominal segments bordered with a fine yellow band, only the fourth abdominal segment is almost entirely a yellow-orange. The legs are black/brown with yellow ends and the head is black with an orange-yellow face. A typical worker hornet is approximately 22mm (1 inch) in length.

There is further information about the biology and life cycle of the Asian hornet on the National Bee Unit website.

Are Asian hornets dangerous? -As with bees and wasps, the Asian hornet has a painful sting. The sting of an Asian hornet is no more harmful than that of a bee or wasp although if a person is allergic to bee or wasp stings they are also likely to react to the sting of an Asian hornet. However Asian hornets may act more aggressively than most other indigenous bee and wasp species if their nest is threatened so it is important not to deliberately provoke them. When foraging for food away from the nest the Asian hornet is no more aggressive than a normal wasp.

Sour fig patch

Sour Fig

Sour Fig (Carpobrotus edulisis) the single biggest threat to Alderney’s coastal habitats. Also known as Ice plant or Sea Fig, it is a robust, flat-growing trailing perennial herb that forms dense mats. The leaves are very green or reddish when older, and succulent, sharply angled and triangular in cross-section, with tiny serrations along the outermost edge. Flowers are solitary and either yellow or pink. Two similar species, Sally-my-handsome, Carpobrotus acinaciformis and Angular Sea Fig, Carpobrotus glaucescen, are also present and invasive in Alderney.

Sour Fig is native to South Africa, but has been introduced to many parts of the world. In Europe it is known from the Mediterranean region and further north in Germany, the UK and Ireland. It was first recorded in Alderney in 1953, but it is thought to have been introduced before this date, as ornamental ground cover. It spreads easily and new patches can form from a very small piece of broken stem. Broken pieces can be moved by rabbits, birds and the wind. Many people, both locals and tourists, also like the appearance of the plant, and cuttings are often taken for gardens. This is likely to contribute to its spread. It is now present throughout the island, in all coastal areas, and poses a major threat to native flora and contributes to coastal erosion.

Sour Fig competes aggressively with native species such as Bastard Toadflax, Small Restharrow, Stemless Thistle and Wild Thyme, and often smothers rare and endangered species. Once established, it spreads quickly and appears to be unaffected by grazing or competition. It is also known to modify soil properties and nutrient dynamics, increasing soil Nitrogen and organic Carbon, and reducing soil pH. This can hinder native flora recolonising after the fig has been removed; and increases the likelihood of scrub species such as bracken and bramble. Finally, Sour Fig can decrease species diversity by preventing sand movement, hindering the natural processes of disturbance and change in dune environments.

NZ pygmyweed


New Zealand Pygmyweed

New Zealand Pygmyweed or Australian Stonecrop (Crassula helmsii) is a perennial with yellowish-green, succulent leaves and solitary white or pale pink flowers. It grows in ponds, lakes, reservoirs, canals, and ditches, as well as on damp mud at the margins of waterbodies. It tolerates a range of pH conditions, from acidic to alkaline and even slightly salty areas.

Native to coastal regions of southern Australia, Tasmania and New Zealand, C. helmsii was brought to Great Britain in 1911 for sale as an oxygenating plant for ponds. It was first recorded growing in the wild in Essex that same year. Its continued spread is almost certainly by vegetative fragments on boats, machinery used to manage waterbodies, clothing and possibly wildfowl. It can root from a mere 10mm of stem. In addition, turions, short shoots, which break off easily, are produced in autumn; and as these float, they are an effective means of colonisation within wetland systems. It is possible that new introductions continue as a result of people discarding pond plants.

New Zealand pygmyweed forms dense mats from 0.5m above to 3m below water level, over many square metres. This shades out other plant species and causes oxygen depletion over the underlying water column. Eventually this leads to a decline in invertebrates such as dragonflies, frogs, newts and fishes - no species are known to preferentially graze C. helmsii. It may cause extensive declines in native plants and prevent recreational and commercial activities.

How you can help


Don’t plant Sour Fig in your garden. Whilst the flowers are attractive, this will only add to the spread of this invasive species. Share the knowledge of the plant’s invasive nature, and the threat it poses to our delicate native plants. Find out more about helping native species and wildlife-friendly gardening on our Wild Gardens page. 

Our friends at Little Island Leaves stock many varieties of native flowers that are beneficial to pollinators and other invertebrates and will make a great addition to your garden.

Report any potential sightings of Asian Hornet in your garden and someone will come to check the species and remove the nest if there is one. Contact the States of Alderney. 


The AWT will run sour fig removal events throughout the year, these are essential if our valuable habitats are to be maintained. Check our Conservation Volunteers page and get in touch to go on the mailing list. 

Sour Fig swamping out native flora

Sour Fig out-competing native flora on the cliffs

What are the AWT doing

Sour Fig Action Plan

The AWT undertook GPS mapping in 2008/9 to chart the distribution of Sour Fig on the island and to identify priority areas for removal. Soil sampling was also carried out to investigate the plant’s impact on soil pH. The results revealed that a total of 206km² of Alderney’s coastline, 2.6% of the island’s total area, is covered by Sour Fig or the other closely-related species. Many of the largest areas covered by Sour Fig are inaccessible due to thick scrub and steep cliffs. When prioritising sites for action, the conservation value of sites affected was taken into consideration so areas of coastal and dune grassland have been selected for targeted action. Main areas we work on include the coastline of the Longis reserve and around Saye and Arch bay. 

Regarding soil tests, results confirmed a lowered pH in areas covered by Sour Fig. This confirms the plant’s ability to alter environmental conditions, and potentially species composition in the long-term. Furthermore, it was observed that insects, such as bees, were not frequently found on the plant. The spread of Sour Fig could therefore have a further adverse effect on the already declining pollinator population.

In light of these findings, the AWT continues to co-ordinate a programme of removal by hand. This is one of the most effective methods of controlling and reducing coverage by the species. Often, large mats can simply be rolled up, but it is important that all plant material is collected, with none left on site. This material must be kept separate from other green waste and it generally burnt. Post-pull raking of the site is recommended to encourage native regeneration. Finally, fig re-growth is expected, and new growth must be pulled in post-removal sites as it appears.

Crassula Action Plan

We undertook an evaluation of the status of Mannez pond, within the Longis Reserve, in 2012. New Zealand Pygmyweed was found to cover 100% of the surface area in some sections of the pond. Native water milfoils were also present, but in lower numbers; and Amphibious Bistort (Persicaria amphibia) appeared to be declining. Invertebrate fauna was dominated by Water Hoglice (Asellus aquaticus), which indicates low dissolved oxygen levels. This could be symptomatic of the high C. helmsii coverage.

With your help we can map and remove invasive species