What are they?
As defined on the GB Non-native Species Secretariat website (NNSS), a non-native species is: ‘…a species, subspecies or lower taxon, introduced (i.e. by human action) outside its natural past or present distribution; includes any part, gametes, seeds, eggs, or propagules of such species that might survive and subsequently reproduce.’
An invasive non-native species is: ‘any non-native animal or plant that has the ability to spread causing damage to the environment, the economy, our health and the way we live.’
Five non-native damselfly and eight non-native dragonfly species have been recorded in Britain as a result of accidental introductions, either as eggs or larvae in imported aquatic plants. Most have been found in the greenhouses of importers of tropical pondweeds. However, at least one species (Ischnura senegalensis) has been discovered at a garden pond, to which it was probably moved with recently imported pondweed. Although unlikely, there is a possibility that these or other dragonfly species could be encountered, particularly near commercial aquatic greenhouses. Some may also emerge from domestic indoor aquaria after sale. As the species concerned have originated in hot climates, it is unlikely – although not impossible – that successful establishment could occur in the wild, as happened with Oriental Scarlet (Crocothemis servilia, pictured right) in Florida, USA.
The incidence of non-native species is related to the origin and extent of trade in pondweeds and water-lillies, and the success of phytosanitary procedures at the point of export and import. Most recent trade appears to centre on Singapore, so common Asian species, such as Common (or Marsh) Blue-tail (Ischnura senegalensis) and Oriental Scarlet (Crocothemis servilia) are more likely to be found. Such species may look very similar to some that occur in Britain; in these examples, Blue-tailed Damselfly and Scarlet Darter respectively. These similarities are confounded because newly emerged specimens or tenerals are most likely to be found.
What is the problem?
Non-native invasive species are considered to be one of the greatest threats to the environment and biodiversity worldwide. Not all species introduced to this country by humans have serious detrimental effects. However, we cannot know which will and which won’t until they have arrived.
Invasive non-native species have already had catastrophic effects upon our wildlife. They predate upon native species, they can spread diseases to native species and they can out-compete native species. Species native to Britain are often ill-equipped to deal with the threats posed by non-native species as they have not evolved to cope with these specific pressures.
Non-native invasive species also have detrimental effects on our ecosystems, interfering with interactions between plants and animals. For example, New Zealand Pigmyweed (Crassula helmsii) is a non-native species to Britain. This plant grows prolifically on the surface of water, smothering the plant life as well as blocking oxygen and light from the creatures beneath.
Often these species are additionally problematic because they spread quickly throughout the country, often aided by humans, such as via walking boots or boat hulls. The problem of non-native species is an ongoing one; once such a species has entered the country it is extremely hard to eradicate it.
Non-native species also have a great economic cost, damaging infrastructure, causing losses of food production, and delaying and creating more work for many industries. For example, New Zealand Pigmyweed also causes flooding with its dense mats of vegetation.
What can you do?
Don’t become part of the problem...
In order to ensure you aren’t facilitating the spread of damaging species, follow the CHECK, CLEAN, DRY campaign’s advice.
Become part of the solution!
Keep an eye out for non-native species when on walks or carrying out dragonfly monitoring, especially near freshwaters as these habitats are particularly vulnerable to the threat of non-native species. In particular, invasive aquatic plants are greatly impacting upon our freshwater ecosystems; any information on their spread can help efforts to control them.
There have been several records of non-native species emerging from domestic indoor aquaria after sale. Therefore, any unusual species found indoors, around houses or around garden ponds need careful checking. Non-native species should not be released into the wild and any individuals must be kept captive. The BDS will try to identify images emailed to the Conservation Officer.
If you are creaing a pond in your garden, remember only to stock it with native plants. These can be obtained from garden nursaries but be sure you are buying a native species and not a similar non-native one. Many invasive aquatic plant species are commonly sold as garden pond plants but native species will serve just as well in your pond without threatening the wider countryside. Our guide, 'Dig a Pond for Dragonflies' gives an outline of those plants to avoid and those which are best for a dragonfly pond.
Visit the NNSS website for details on the identification of non-native invasive species in Britain, how to record them and for more on biosecurity.
Crocothemis servilia (Oriental Scarlet). © nomadicimagery