Soil Animal Days 2021 kick off on NIOO roof

Slak op het NIOO-terrein (Bodemdierendagen 2021)
© Perro de Jong / NIOO-KNAW

Soil Animal Days 2021 kick off on NIOO roof


The seventh edition of the annual Soil Animal Days has been launched from NIOO's green roof. The theme this year is the double lives of soil animals, above- and/or belowground. There's another important duality as well: many soil animals are in decline. For them, it may soon be do or die.

Launch of the Soil Animal Days 2021 (Dutch)

Last year was an unusual year for soil animals. Earthworms, important ambassadors of healthy soils, were found in no less than 84% of participating gardens: more than enough to propel them from third place in 2019 to the top spot in 2020. Woodlice, on the other hand, failed to maintain their previously dominant position in even a single type of garden, for the first time since counting began.

Weatherwise, 2020 turned out to be a year of extremes: first dry for a long time, then very wet and on average always warm. This was 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 played tricks on the woodlice last year. They don't tolerate drought very well."

Worms and spiders

2021 is shaping up to be a very different year yet again. Soil animal expert Gerard Korthals from the Centre of Soil Ecology - which was set up by NIOO together with Wageningen University - picked NIOO's green roof to carry out the first official soil animal observation of the new edition, which started on 24 September.

Green roofs may be green, Korthals noted, but when it comes to soil animals they're no match for other garden types. Another sampling carried out at the NIOO food forest turned out to be much more fruitful.

"Belowground did better than aboveground" said Korthals, even though many soil animals spend their time both below- and aboveground depending on the seasons, their stage of development or other factors. 

But even in the food forest, spiders and earthworms were conspicious by their absence this year, Korthals found.  "A result, no doubt, of the dry weather we've been having lately." What other findings await this year? Which soil animals will turn out to be abundant, and which ones are in the danger zone?

Great expectations

Last year, the number of human participants in the Soil Animal Days was significantly higher than in previous years: 1188 people submitted their observations via

"They were truly Soil Animal Days XL", says Gerard Korthals. In previous years, many people went looking for soil animals in groups. But last year, a higher percentage went solo - which may well have been due to the pandemic.

Between them, the participants counted an unprecedented 17,500 soil animals: "another record" according to Korthals' colleague, Ron de Goede from Wageningen UR. After six editions of the Soil Animal Days, this now brings the total number of soil animals found and counted to nearly 53,000.

Interest in soil animals in the Netherlands continues to grow, so we're hoping that last year's record may be broken again this year. So if you're in the Netherlands or know anyone who is, just follow the instructions on this page to participate to submit your results!

The deadline this year is 6 October.

Zevende editie

Voor de zevende keer organiseren het Nederlands Instituut voor Ecologie (NIOO-KNAW) en het Centrum voor Bodemecologie het citizen science-project de Bodemdierendagen. Ze doen dat met hulp van onderzoekers van Wageningen University & Research en de Vrije Universiteit, plus een groeiend aantal partners. Op steeds meer plekken in Nederland brengen ze met het publiek het bodemleven in kaart. Met de resultaten van de eerste zes edities was vorig jaar de conclusie dat groene tuinen en parken een belangrijke rol spelen bij het in stand houden van de stadsnatuur.

  • Perro de Jong / NIOO-KNAW
  • Perro de Jong / NIOO-KNAW
  • Perro de Jong / NIOO-KNAW