We used seven sources of data: 1. pinned specimen records from the Natural History Museum of Denmark, 2. pinned specimen records from the Natural History Museum of Aarhus, 3. specimen records from the Natural History Museum of Stavanger, collected by Holger Holgersen, 4. observation records from AntWeb collected by Sämi Schär, 5. observation records from Christian Skøtt, 6. observation records from the EuroAnts course and 7. preserved specimen records from the Ant Hunt. These were manually georeferenced and cleaned so that we excluded detections of unidentified species, those without collection date or geographic coordinates and non-native species. Using ArcGIS, remaining data were binned into 10 x 10 km grid cells and 10 year time-periods (decades). The raw data sets are available from GBIF: Calabuig I (2014). Danish Ants (Formicidae). Zoological Museum, Natural History Museum of Denmark. Occurrence dataset https://doi.org/10.15468/xcwkfb Simonsen T, Sheard J K (2021). Natural History Museum Aarhus Ant Collection. Version 1.2. Natural History Museum Aarhus. Occurrence dataset https://doi.org/10.15468/wp3kzr Fiskå A (2018). MUST, Insecta. Version 9.266. Museum Stavanger. Occurrence dataset https://doi.org/10.15468/zkm8mj Fisher B, Fong J (2021). AntWeb. California Academy of Sciences. Occurrence dataset https://doi.org/10.15468/wqmjjt Sheard J K, Nielsen, M G, Pedersen, J (2020). Skoett Ant Collection. Center for Macroecology, Evolution and Climate, University of Copenhagen. Occurrence dataset https://doi.org/10.15468/2xh5fd Sheard J K, Nash D R (2020). Euroants. Department of Biology, University of Copenhagen. Occurrence dataset https://doi.org/10.15468/jpacce Sheard J K, Sanders N, Dunn R, Rahbek C (2021). The Danish Ant Hunt. Version 1.9. Center for Macroecology, Evolution and Climate, University of Copenhagen. Sampling event dataset https://doi.org/10.15468/dcijnc

The combined, cleaned dataset is uploaded as Dataset.csv. The scripts zipfile contains the R code used to run the analysis. The analysis_outout zipfile contains files needed to run the analysis and produce the figures. The results zipfile contains the results of the occupancy models. The README.pdf contains an explanation of all dataset files and scripts uploaded to Dryad. Funding provided by: Danmarks GrundforskningsfondCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001732Award Number: DNRF96Funding provided by: 15. Juni Fonden*Crossref Funder Registry ID: Award Number: Funding provided by: Knud Højgaards FondCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100009938Award Number: Funding provided by: Augustinus FondenCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004954Award Number: Funding provided by: Beckett-FondenCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100009898Award Number:

We combined participatory science data and museum records to understand long-term changes in occupancy for 29 ant species in Denmark over 119 years. Bayesian occupancy modelling indicated change in occupancy for 15 species: five increased, four declined and six showed fluctuating trends. We consider how trends may have been influenced by life-history and habitat changes. Our results build on an emerging picture that biodiversity change in insects is more complex than implied by the simple insect decline narrative.