Problems Caused by Invasive Insect Species in the UK
Do you hate insects and run screaming from the room if you see a spider? Well like them or loathe them, these insects are a very important part of our environment and undertake some very valuable tasks in any eco-system.
Some insects pollinate flowers so that they can produce fruit, some eat their way through dead vegetation, breaking it down and helping to keep forests and woodland clear, and some are an important part of the food chain.
Like animals, insects have evolved and adapted to local conditions, and there are some insect species that only exist in very small areas.
So when an invasive insect species arrives in an area and establishes itself, it can prove to be very damaging to the native insects, and can also adversely impact the local plants, trees, animals, marine life and even us humans.
Because they are so much smaller than most animals, these introduced bugs find it a lot easier to hitch a free ride on a ship, lorry or plane and are much harder to detect and keep out.
There has been many a news story about an unsuspecting person who finds an uninvited tropical spider in the bananas that they have just bought at the supermarket or is shocked by the sight of a scorpion crawling out of their suitcase after returning from a long-haul holiday.
Oak Processionary Moth Caterpillars
Of course, many of these are solitary individuals and cannot form a breeding population, but if a nest or group of insects is inadvertently brought into the country they can, if the conditions are right, establish colonies or nests and start reproducing.
As many insect species breed very rapidly and in great numbers, they can quickly spread over a wide area.
Quite often the invasive species will be able to out-compete the local insects, as they may be bigger, more aggressive or voracious feeders who deplete the food supply.
They are also more likely to have no natural predators, and can even bring previously unknown diseases and parasites into an area that can devastate native species.
You may be surprised to learn that some invasive insects have been deliberately introduced as a form of environmentally friendly pest control, with their numbers then exploding out of control and causing more damage than the benefits they were supposed to bring.
So let’s have a look at some of these insect invaders and see what damage they are causing.
The Harlequin Ladybird
Perhaps the best known of these invasive species is the Harlequin Ladybird that has taken up residence in many of our gardens and homes.
They are also known as Multicoloured Asian Ladybirds or Halloween Ladybirds, and tend to be larger and more aggressive than our forty six native ladybird species.
They are native to north-eastern Asia, but were introduced into the United States during the 1980s and then into Europe as a form of pest control, their favourite foods is aphids.
They first appeared in southeast England in 2004, where they had arrived accidentally, and have proved so successful that they can now be found as far afield as Scotland and Northern Ireland.
As they are such voracious eaters they are threatening many native insect species, such as native ladybirds, butterflies, and lacewings, as they chomp through vast quantities of their eggs and they also have a huge appetite for our native aphids.
These aphids were the reason they were introduced into the US and Europe as pest control, because if an aphid colony grows too large, the ‘honeydew’ they secrete begins to grow a fungi called sooty mould that blights the leaves of the plant.
They also breed several times a year and have few natural predators in Britain, which also helps them to out-compete our native ladybirds.
Introduced Harlequin Ladybirds are also not good news for us humans, as they get into our houses, and in the autumn months can swarm in numbers over internal walls and attics as they look for somewhere safe and cosy to spend the winter.
Unfortunately, they are not good guests when they arrive as they spray a nasty, yellow toxic chemical around your home and they are biters, which can cause an allergic reaction in some susceptible individuals.
However unpleasant they may be if they get into your home, experts are not encouraging us to kill them because their appearance is so variable that we might kill a native ladybird by mistake, reducing their numbers even further.
The Oak Processionary Moth
This uninvited invasive moth is particularly unwelcome, as not only does it damage the oak trees that it infests, but is a severe health hazard to both people and pets.
As a moth, part of its life cycle is a caterpillar stage and the reason they are called the Oak Processionary Moth is because their caterpillars buddy up in groups of around 200 and systematically munch their way through the leaves of their host oak tree, causing a lot of damage.
The ‘Processionary’ part of the name comes from the behaviour of these groups of caterpillars, who follow each other around the leaves and branches in long columns.
It is these caterpillars that are such a danger to people and animals, as they grow around 62,000 highly toxic long hairs which if you come into contact with them can cause some very unpleasant symptoms such as rashes, sore throats, streaming eyes, vomiting, problems with breathing, fever and dizziness.
But the most devastating thing that they can trigger is severe asthma attacks, which could potentially kill someone.
These toxic invaders originated in Southern Europe, and have slowly worked their way north, arriving in London in 2006. Initially the Forestry Commission attempted to eradicate the Oak Processionary Moth by issuing statutory notices to land owners with infested oak trees requiring them to have caterpillars and nests removed and destroyed.
But controversially abandoned their attempts in the spring of 2011 in favour of trying to contain the spread of the hairy menace to the areas where they have already established themselves mainly in south west London.
Experts are worried that the problem might become so great that children will have to be stopped from playing in areas where there are infested oak trees and people will not be able to let their pets out.
In the Netherlands and Belgium the Oak Processionary Moth has become such a threat that the nests and caterpillars are sucked from the oak trees by giant vacuums and then incinerated at very high temperatures.
Horse Chestnut Leaf Miner
This invader moth was totally unknown to science until the late 1970’s when it was found in Macedonia and was recognised as a new species of Cameraria in 1986.
The Horse Chestnut Leaf Miner then somehow managed to travel to Austria in 1989 and then spread through central Europe and on to the north and south of the continent.
They arrived in the UK in the summer of 2002 when it was realised that the moths and their larvae were infesting the horse chestnut trees on the edge of Wimbledon Common in the south west of London.
They spread rapidly and are now to be found in horse chestnut trees across much of South East England, East Anglia and the Midlands.
So why are these moths so destructive? The horse chestnut is one of Britain’s most iconic trees, providing the conkers that most of us played with in our childhood (and maybe older!) years, but the tiny larvae of the Horse Chestnut Leaf Miner burrow into the leaves of these beautiful trees causing them to go brown too early in July and August.
If the leaves get attacked too frequently the tree itself will become damaged and will become stunted and withered. It is not the leaf miner larva that actually kills the trees, it is a fatal tree disease called bleeding canker that kills them, but experts think that it is the damage caused by the Horse Chestnut Leaf Miner that makes the horse chestnuts more vulnerable to infection.
The arrival of this invasive insect in Britain also seemed to unfortunately coincide with a newer, more virulent form of the bleeding canker appearing. This disease is a bacterium that causes lesions on the horse chestnut’s bark that ‘bleed’ a reddish, brown sticky fluid. If the disease advances too far around the trunk it can prevent the vital nutrients that the horse chestnut needs to survive flowing around the tree.
It is also thought by the scientists that the leaf miner also somehow manages to reduce the horse chestnut’s immunity to the bleeding canker. There is currently no cure for the disease and it is estimated that as many as half of all our horse chestnuts have already been infected, and we could lose all of them in twenty to thirty years.
Many of the infected trees are felled, as the weakened branches and trunks become a danger to the public, especially in high winds. New horse chestnut saplings are also not being planted, so the dead trees are not being replaced, and different tree species are being planted where these majestic trees once stood.
There is one method that is being used to try to repel the Horse Chestnut Leaf Miner invasion, and that is clearing old leaf litter from around the base of the trees. This is being done because the leaf miner moth lays its eggs in the litter and this might prevent it breeding so prolifically.
The smaller the invader, the easier it is for them to get in under the radar, and the Argentine ant has managed to establish itself in our back gardens almost unnoticed.
They have reached our shores all the way from South America, by hitching a free ride on ships and planes. They are known as perhaps the most prolific invasive species in the world, as they have established themselves in Asia, North America and Europe.
Unlike most ant colonies which are highly territorial and will aggressively attack any invaders; these Argentine ants seem to have all originated from a single colony and go on to form super colonies where the ants do not fight each other and can remain peacefully in the same area.
There are now some truly vast super colonies of Argentine ants spread across California and Japan and an astonishing one that spreads for 4,000 miles around the coast of the Mediterranean Sea.
You might not realise that they have taken up residence in your garden, because they do look very like our native garden ants being light brown in colour and being between 2mm and 3mm long. However, they are very bad news for our native ants as they are a much more aggressive ant species and they destroy native ant nests when they are establishing their colonies.
They have a very sweet tooth and milk aphids for the sticky, sugary secretion they produce called ‘honeydew’ and they out-compete the native ants for food.
They are another invasive insect species that likes to move uninvited into your house, and will build their nests under the floorboards, under kitchen appliances such as cookers and get into your cupboards.
Unlike our native ant nests, which only have one queen producing eggs, the Argentine ant colonies can have up to eight and if they are sprayed with the usual ant powders and chemical insecticides only the worker ants will die, and the queens will just scatter and go and form new colonies, actually increasing the numbers of these invaders rather than destroying them.
One of the few ways to be rid of them is to put down bait laced with insect growth regulator, which when the bait is taken by the workers to the nest will inhibit the growth of the immature ants.
To try and stop them getting into your house it is recommended that any vegetation surrounding your home is cut back, as the moisture in plants seems to attract Argentine ants and also to try and seal any holes or cracks in your exterior walls.
Now these are only a very few of the invasive insect species that are now living and spreading across Britain, and they all have an impact on our environment. We are losing our native insect species, trees and in some cases our health is even being threatened by these invaders.
Invasive species are also a drain on our economy, as it costs a lot of money to try and eradicate or contain them, and doing things like replanting trees is also very expensive. Unfortunately, there are no easy answers and the best thing would be to prevent them from being brought into the country in the first place.
Oak Processionary Moth Caterpillar image Arturo Reina Wikimedia Creative Commons Share Alike 3.0 Unported Attribution