What is an invasive species? Some emblematic examples

“Invasive” is a term whose meaning is not clear on first reading because it is an Anglicism. The corresponding French term is “invasive”. The term “an invasive species” may be better understood, but is not entirely synonymous. Here, let’s take a look at what an invasive species is and discuss some emblematic examples.

The threat of invasive species

The term invasive species is used to designate a local species that has a strong colonizing power, either because it grows rapidly, or because it reproduces very quickly. In our gardens, the most emblematic of these species are dandelions, quackgrass, bindweed and clover.

An invasive species is first of all a species, animal or plant, which settles and develops outside from its native environment. The species has been introduced voluntarily or involuntarily, enjoys its new ecosystem and develops, to the point of competing with local species and causing environmental, economic or health nuisances. Indeed, these species often benefit from greater resistance than local species, which can carry diseases that disseminate other species, or from the absence of predators that regulate their presence in their sites of origin. Invasive species are therefore one of the primary factors in loss of biodiversity in the world.

American crayfish

In France, 3 kinds of crayfish are identified as invasive, all from North America. They were imported for breeding but the relative porosity between breeding and natural environments has led to their propagation in rivers, lakes and bodies of water.

The American crayfish (Orconectes limosus) is arguably the most common. Bigger and more resistant than the local crayfish species, it was an advantage for breeding. Alas, she is very voracious. Moreover, it turned out healthy carrier from the crayfish plague which is now decimating the native crayfish populations. Finally, once an adult, she is only afraid of large predators such as pike, pike perch, eel, otter or heron. But as soon as these are less present, it multiplies rapidly, consuming large amounts of food, which considerably impoverishes the life of small ponds or streams.

The most effective way to fight American crayfish is to fish them, which is all the more enjoyable because they are edible. As for all other fisheries, you must have a card and respect the opening periods of the first category activity.

It is necessary to be attentive and cautious in the event of practice in waterways likely to shelter populations of crayfish with white legs which it is necessary at all costs to preserve. The main key to identifying the American crayfish is the shape of the claws and the head. It is absolutely necessary to release the other species. In addition, it is essential to disinfect the equipment before and after fishing so as not to carry crayfish plague. To do this, just soak it in lightly bleached water and rinse.

The Asian hornet

We noted the presence of the Asian hornet in France in 2004. It was imported involuntarily, in favor of deliveries from Asia. And the heat wave of 2006 would have given a decisive impetus to its development. In 7 years, it has spread over more than half of French territory, some experts advancing the distance of 100 km per year as a rate of progression.

The Asian hornet is considered an invasive species because of this rapid rate of spread but also because no predator is slowing down its proliferation. It is aggressive with other species and in particular consumes bees whose populations are already very fragile. In rural areas, these represent 40% to 50% of their diet and in urban areas, up to 80%. In addition, he turns to caterpillars, butterflies, spiders and flies.


The nutria is a pretty nice looking myocastor. For city dwellers strolling around bodies of water, the observation of living animal species such as nutria is a pleasure. It is therefore difficult to understand that its presence is harmful and that this species must be the target of measures to limit the population.

Originally it lived in South America and was introduced to Europe in the 19th century to develop farms of fur cheap. It measures 40 to 60 cm in length, with a tail of 25 to 45 cm. Novices might take him for a beaver. It is a herbivorous rodent but it adapts quickly to the resources provided by its environment, thus being able to consume freshwater mussels.

Why is it considered an invasive species? When young, nutria can be preyed on by martens, buzzards or barn owls. But once an adult, it has no natural predators. However, it degrades the banks, promoting their erosion, threatens certain aquatic plant species, destroys the nests of aquatic birds and carries diseases such as leptospirosis.

It can be shot with a rifle, an arch, or a trap. Poisoning with anticoagulants, a time used, is now prohibited because the method was not selective enough and killed other animals. When present in reasonable amounts, it can play a positive role in the development of marsh vegetation such as reeds and duckweed. So there is a real balanced to find with this animal to succeed in developing a harmonious cohabitation.

The sacred ibis

Living in ancient Egypt, the sacred ibis had happy days in sub-Saharan Africa and Iraq before being introduced in Europe, and in particular in France, in zoos, at the end of the 80s. escaped, one of the main outbreaks identified being the Branféré park in Morbihan, which organized free flight shows with this bird.

This bird has great ability to adapt to its environment. In a little over 10 years, between 1990 and the 2000s, the sacred ibis population increased from 20 to 5000. It lives in wild colonies near the coasts, and it is also found a lot on the banks of the Loire. He eats seeds, fish and proves to be quite capable of rummaging in trash cans.

In 2013, the Ministry of Ecology seized on the problem and decided to eradicate it in Loire-Atlantique. It threatens in particular the terns whose eggs it gobbles. Campaigns of hunt were organized, sometimes shocking the inhabitants. But it is the fact of having taken into account the problem too late that led to these extreme measures. There was a short moment of balance during which the cohabitation with the other waders was peaceful. And then the imbalance of fauna, flora and human activities gradually set in. Today, it is mainly in Italy that its presence poses major problems.

Ecosystem balance

Man aspires for species to live in a stable interaction. However, as life is movement, it is a dynamic balance that must be found, requiring fragile and constant adjustments.