Soil animal days

First held in 2015, the Soil Animal Days are an annual citizen science project organised by the Netherlands Institute of Ecology (NIOO-KNAW) together with the Centre of Soil Ecology (CSE) and a growing number of partners. Soil animal experts from NIOO, Wageningen UR and Amsterdam's VU University are responsible for drafting the special soil animal chart that participants can use for their observations. 

Every year in or around October, people all over the Netherlands go out into their gardens, and entire classes go exploring their schoolyard. So if you're in the Netherlands and have access to a garden, park of schoolyard, you can join our citizen science project by downloading the chart from this website and looking for soil animals.

The project's results help scientists establish how well soil animals are doing in Dutch cities and towns. Without a healthy number of soil animals, there can be no healthy soil - and that would have grave consequences for food production and biodiversity, among many other things.

Earthworms vs woodlice

Some years turned out to be a year of extremes, especially weatherwise: dry for a long time, or on the contrary very wet. This latter may be to the earthworm's advantage and the woodlouse's detriment, suggests woodlice expert and Soil Animal Days stalwart Matty Berg from Amsterdam's VU University. "The weather indeed plays tricks on the woodlice. They cannot tolerate drought very well."

Earthworms, therefore, were the overall winners after a number of years in which the woodlouse was the odds-on favourite. Meanwhile, the number of human participants are significantly higher than before. "These are truly Soil Animal Days XL", says organiser Gerard Korthals from Wageningen UR and previously the Netherlands Institute of Ecology (NIOO-KNAW).

Between them, the participants counted an unprecedented 21,000 soil animals last year: "another record" according to Korthals' colleague, Ron de Goede from Wageningen UR. After nine editions of the Soil Animal Days, this now brings the total number of soil animals found and counted to more than 100,000.

Overall conclusions

So are there any general conclusions to be drawn after nine years of Soil Animal Days in the Netherlands? Gerard Korthals and his fellow soil researcher Ron de Goede answer in the affirmative. "Green and half-green garden, and parks and public gardens, are eldorados for earthworms, snails, spiders and woodlice in particular." These groups of soil animals are found in more than 80% of the gardens belonging to one of those types.

Another conclusion is that the weather is indeed an important factor when it comes to the survival and level of activity of soil animals. In 2017, arachnids came out on top after a wet season while in 2018 - a dry year - there were lots of woodlice and few slugs. "We can conclude that in dry years, in particular, the type of garden and the way in which it is maintained are key factors for the survival of soil animals in the city."

So how about the future? Will 2024 be another unusual year for soil animals? Find out with us between 20 September and 7 October, when the Soil Animal Days return for the tenth edition!

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