Farmers, beekeepers are grappling with alien hornets, geese and frogs

From Egyptian geese at lakes to Asian hornets in trees and bullfrogs in ponds, invasive species present a growing challenge to farmers, beekeepers and conservationists around the world.

"Invasive species are only a small proportion of neozoa, but they can cause massive problems," says Lisa Tippelt, a nature conservation officer in Germany.

Animal species have been colonizing areas through human intervention - dubbed neozoa - since the beginning of intercontinental trade at the end of the fifteenth century.

The number of new forms of life causing problems is quite small. Tippelt says around 10% of new species can survive in their new environment and of these, only around 10% become established and of these, only around 10% are invasive species.

But that is enough to cause problems. The European Union published a list of invasive alien animal and plant species of EU-wide importance for the first time in 2016 and now provides regular updates.

The list shows 37 invasive animal and plant species (including 23 neozoa) have now become 88, of which 47 are neozoa, Tippelt says.

In the south-western German state of Rhineland-Palatinate, Asian hornets are a concern as they are eating more and more honey bees.

The first nest of Asian hornets was discovered there in 2014; by 2023, more than 1,000 had been reported, Tippelt says, noting the increase came after a call for reports so officials could take action against the insectivores.

The species most likely came from China and was brought into France in a consignment of goods in 2004, officials say.

In Rhineland-Palatinate, it is now concentrated in the Upper Rhine plain with Frankenthal, Speyer and Worms, though the hornets can be found in large parts of the state - and are everywhere in neighbouring Saarland, she says.

In summer, the colonies move to a second nest, often in trees up to 30 metres high. Their hemispherical nest has a diameter of around 80 centimetres and a colony can contain up to 2,000 Asian hornets - compared to the 400 to 700 in a local nest.

"Asian hornets are very hungry and are more manoeuvrable than our native hornets, as they can also fly backwards," says Tippelt.

A further invasive alien species is Egyptian geese which can be highly aggressive. "In some cases, they drown other chicks, such as mallard ducks," says Christian Dietzen from the country's bird protection centre. "The species has the potential to pose a threat to other species."

The EU listed them as an invasive species in 2017. They cannot be imported, bred, transported, commercialized, used, exchanged or intentionally released into the environment and member states must try to eradicate the species.

The Egyptian geese population has been increasing since the 1980s, and the birds are particularly prevalent along rivers such as the Rhine and Moselle.

The geese are particularly noticeable when they have young and then - like other geese - join up with other families. During the winter months, 500 to 600 geese can gather. "Canada geese concentrate more in certain places and don't migrate as far as Egyptian geese."

From a conservation perspective, however, Egyptian geese are not a problem, despite their proliferation. "No other species is threatened in its population."

But they are clashing more and more with humans at swimming pools, golf courses and sunbathing lawns, Dietzen says. Add Canada geese and greylag geese to the mix and the birds could cause serious damage to crops.

Germans may hunt the geese but not in residential areas. "That's part of the problem because they notice this and particularly like to stay there."

Parakeets too are a nuisance, some say, though the vibrant green birds are not officially listed as an invasive species, moving throughout western Germany from the Bonn-Cologne area.

One species that is harming other species is the 15 to 20-centimetre North American bullfrog, which Tippelt says has a "major negative impact" on biodiversity.

"It eats everything it can get its hands on and is therefore also a major food competitor for our native frogs, which are only around 6 centimetres in size."

They can also transmit a fungus that leads to skin diseases in amphibians. The bullfrog is particularly widespread in the southern Palatinate's Rhine floodplains and stagnant bodies of water. More than 1,000 have been gathered, plus larvae and spawn and some ponds have been fenced off.

Large and invasive crayfish are also a concern in waterways as they transmit fungal diseases and cause crayfish plague, says Fulgor Westermann, an aquatic ecologist at the state environmental office.

Currently, four crayfish species from the EU list have also been detected in Rhineland-Palatinate, including the camber crayfish, the signal crayfish and the Louisiana swamp crayfish.

The highly reproductive calico crayfish is not yet on the list - but "can destroy the entire plant and animal world in small standing waters because it eats everything until the area is completely empty," says Westermann.

"Prevention is very important with invasive species," says Tippelt - which means sensitizing the population and beekeepers to make sure they do not feed invasive species,

"The best way to combat invasive species is when there are only a few animals," she says.