Invasive species : The Asian Hornet in France

The Asian hornet (Vespa velutina), has colonized France and is spreading in Europe, this species acclimatizes easily to new territories and reproduces very quickly, thus making numerous ravages to bees and other pollinating insects. We find this species in the north of India, in China and in the mountains of Indonesia; it usually lives in gardens and green spaces and feeds on social insects. The Asian hornet is mainly black, with a broad orange band on the abdomen and a yellow first segment. Its head is orange, seen from the front, and its legs are yellow at the ends. It measures between 17 and 32 mm. It is smaller than the European hornet.

It seems to have arrived in France hidden in a shipment of Chinese pottery delivered in 2004 to Tonneins (Lot-et-Garonne). In a few years, it has proliferated all over France and has also spread to Spain and Portugal. Vespa velutina has spread to 24 regions from the Charente-Maritime to the Gard. Researchers have observed through genetic studies that samples taken from different nests had the same DNA sequence. So the hornets studied all have the same genetic characteristics; this means that a single mother would be the origin of all the Asian hornets present in France today. It took the arrival by chance of a single Asian hornet queen to spread this invasive species.

The proliferation of this species is very fast, indeed a nest gives four nest the year after. Moreover, there are not a lot of predators of the hornet in Europe, allowing them to cause significant harm by attacking bees. Bees constitute 80% of the hornets' diet. Nectar harvests and pollination are then strongly impacted. The hornet will cause the loss of many bee colonies by decreasing their activity but also by stressing them, leading many times to the death of these insects. The Asian hornet is therefore a major threat to European biodiversity, preventing the reproduction of many species of flowering plants due to the lack of bees. Hornets also cause damage in orchards by eating fruit, they recover the sugar present in the fruits causing them to rot. Leading to a decrease in the quality of the products in the wine sector. The proliferation of Asian hornets poses a health, economic and agricultural problem.

05.05.2022

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Don’t be shellfish – the invasive crab that isn’t too invasive

Not all invasive species are equally invasive. Sometimes, species find an opening in local ecosystems adding to local biodiversity without larger disruptions to local wildlife.

The white-fingered mud crab (Rhithropanopeus harrisii) is a small crab named after its claws that are white underneath. It is originally from the Atlantic coast of North America but has become one of the most widely spread crab species globally. It was first observed in Finnish waters in 2009 in Naantali, in southwest Finland. Since then, the crab has spread steadily and has become a common sighting all over the Archipelago Sea (figure 1).

It is said that invasive species are bad for the local environment but is it true? The jury is still out on the mud crab. The crab seems to be very successfully in adapting to different surroundings. Typically, it lives on soft, muddy bottoms but in the Archipelago Sea it has also adapted to live on rocky bottoms among the bladderwracks.

As a predator, the non-native crab could potentially affect native species drastically. The crab has adapted to feed on a variety of local species, including amphipods, mussels, and small fish. It seems to be especially fond of the Theodoxus fluviatilis, snails that clean the bladderwrack from algae. However, it looks like the presence of the white-fingered mud crab does not have any considerable effect on the populations of local species or that the bladderwrack would be affected by the diminishing of the snails.

The crab is food for others, once they get the taste for it. The cormorants, perch, and four-horned sculpins have already found the crab a tasteful addition to their diets, as indicated by stomach content studies of these species. Probably though, the crab will not end up on our plates.

The crab is here to stay whether we like it or not. It seems it has found its own niche to fill in the ecosystem of the northern Baltic Sea, finding it’s place in the food chain while not disrupting the life of the other species around it. Long term effects of the crab remain to be seen, but for now, luckily, the biggest hazard from this newcomer for locals is the possibility of being pinched in the toe when having a swim.

Camilla Arhippainen & Marcus Pellas

References:

Forsström, T., Fowler, A.E., Manninen, I., Vesakoski, O. (2015) An introduced species meets the local fauna: predatory behavior of the crab Rhithropanopeus harrisii in the Northern Baltic Sea. Biol Invasions (2015) 17:2729–2741

Fowler, A.E., Forsström, T., von Numers, M., Vesakoski, O. (2013) The North American mud crab Rhithropanopeus harrisii (Gould, 1841) in newly colonized Northern Baltic Sea: distribution and ecology. Aquatic Invasions (2013) Volume 8, Issue 1: 89–96

Havaintokartta (n.d.) https://vieraslajit.fi/havainnot?taxonId=MX.53034 Visited 1.4.2022

Puntila-Dodd, R., Loisa, O., Riipinen, K., Fowler A.E. (2019) A taste for aliens: contribution of a novel prey item to native fishes’ diet. Biol Invasions 21:2907-2917

04.05.2022

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