There is a new species in the Netherlands: the plague ant Lasius neglectus. But it's been in Wageningen for 23 years: in a specimen jar at Alterra.
Mabelis first got hold of the ant in 1986, when some Leiden residents called him up about a large colony of ants that was bothering them. According to an inspector from the Environmental Health department, the ants were of the Lasius alienus species. But Mabelis saw at once that this wasn't right. 'L. alienus behaves quite differently. This was a large colony with many queens, and L. Alienus only has one queen. What is more, the young winged queens didn't fly off to settle elsewhere.
It had to be another species, Mabelis concluded. 'But which one? I couldn't figure it out. And I didn't for one moment consider that it could be a new species.' That penny dropped a couple of years later when André van Loon of the European Invertebrate Survey, the Netherlands wrote an article about a new ant species he had discovered in Budapest. 'Then it was clear to me: That's the one. Straightaway I changed the label on the jar. "L. neglectus? Instead of L. alienus???" The question mark stayed there because my classification had to be verified.'
Mabelis reported his find to his colleagues in the ant working group of the Entomology Association. 'But no verification came. Nobody picked up on it.' And so it remained unknown that a plague ant had colonized our country as early as 1986. The ant was drawn to Mabelis's attention again only late last year when several newspapers reported that it was marching on our borders. 'Journalists phoned to ask if it had already been seen in the country.' Mabelis said it was not known. A white lie. After all, there was still no verification.
Verification took place at last when Mabelis had to go to the university of Ghent. 'I thought, I'll take that jar with me.' The Ghent expert Wouter Dekoninck confirmed that it was the plague ant. Then Mabelis told Van Loon about its presence in the Netherlands, and they appeared together on TV in Vroege Vogels, to talk about the ant.
The Ministry of LNV has even commissioned a risk analysis on the plague ant, written by Van Loon. Mabelis says there is no cause for alarm. 'Besides Leiden, the ants have only been spotted in Son, Maastricht, Wassenaar and Katwijk. They would only be a nuisance if they invaded a house en masse. They do that in winter to get out of the cold and in summer to cool down.'
Footnote: the plague ant
The plague ant probably invaded Europe from central Asia. It must have hitched a lift, because it is not a flying ant. Experts say this exotic species has been in the country for several decades but has escaped notice. It looks very like the common ant. The plague ant owes its name to its habit of invading houses seeking warmth in winter or coolness in summer. Mabelis says there is no cause for alarm. Outside a few big towns, the ant has hardly been spotted.