Too much nitrogen in the environment from excess manure has killed off  30% of butterflies in the Netherlands, the AD reports.

Researchers Michiel Wallis de Vries from Wageningen University and nitrogen expert Roland Bobbink have found that butterflies’ habitats have been steadily deteriorating over the last 20 years.

Of the Dutch red list of endangered butterfly species, 17 have disappeared altogether. The numbers of another 23 species, not on the list, have been falling as well.

‘Important species such as the tree grayling used to be widespread but now it can only be found in the Veluwe area.  Alcon Blues, which used to live in grassland, are now only spotted in wetlands and there too their number is falling,’ they told the paper.

Nitrogen is produced by industry and traffic but the main culprit is agriculture. Wallis de Vries thinks that a 2015 agreement on limiting excess manure does not go far enough.

‘In the end agriculture will have to become sustainable in the interest of everyone. The rapid decline in bio diversity shows it will have to happen sooner than later,’ he told the paper.