City Nature Expedition

How many species of plants, animals and fungi live in urban nature? in 2026 are Leiden, Leiderdorp, Oegstgeest and Katwijk observing and recording how many unique species there are, to put the state of urban nature on the map. Together everyone from May 1st till 30th of June will record every spider, snail, mushroom or dandelion they come across during ‘Expeditie Stadsnatuur ’. The goal of the 2026 edition is to find at least 26 hundred unique species.

Observing is knowing

With Expedition Stadsnatuur, the Leiden Biodiversity Network (LBN) is calling on Leiden, Leiderdorp, Oegstgeest and Katwijk to record urban nature and monitoring it. This is done by observing and recording as many species using the Obsidentify app. These records will not only show us the variety of different species living in Leiden, but also show what areas need help and what local initiatives help the biodiversity. All of the observations recorded will be made visible on waarneming.nl.

Where can you observe and record biodiversity?

In streets, parks, (vegetable) gardens, at school or at home, anywhere within the limits of Leiden, Leiderdorp, Oegstgeest and Katwijk. Species can be found above and below ground, on tree trunks and flower petals but also under paving stones or on your bedroom wall. Every species in Leiden counts - apart from people, pets, house or garden centre plants.

Help us put Leiden biodiversity on the map!

The more unique species we record, the better, and the more people who can join us the better as well! From schoolchildren to students, from vegetable gardeners to balcony owners. Whether you are 7 or 107 years old, every resident or visitor to Leiden can participate. Alone or in clubs, with or without knowledge of nature, together we will map all plants, animals and fungi living in Leiden. You can go on a nature expedition with your class, club or street or on your own. Or join one of the free city expeditions in your neighbourhood.