This archive contains pre-processed datasets used for the analysis of species occupancy models, the results of which were used in the calculation of multi-species indices as part of the regional WWF Living Planet Index for Belgium. The datasets are csv files (comma separated and . as decimal mark). For each species group (moths, butterflies and grasshoppers), the following files are available: a species list (files with 'species' in the name) an observations list (files with 'observations' in the name - for butterfly or moth species with two distinct flight periods, also a file with the data for the second generation is available) For one species, Fabriciana adippe, separate files are available with corrected data. The species list files contain the following variables: species_id (unique species id) scientific_name (accepted scientific name according to the GBIF taxonomic backbone) species_name_NL (Dutch species name) species_name_FR (French species name) season_start (n-th day of the year that marks the beginning of the first -and possibly only- generation) season_end (n-th day of the year that marks the end of the first -and possibly only- generation) The observations files contain the following variables: species_id (a unique identifier) year (year of observation) month (month of observation) day (day of observation) julian_day (n-th day of the year) site_id (unique identifier for the 1 km x 1km EEA 1 km x 1 km reference grid square https://www.eea.europa.eu/data-and-maps/data/eea-reference-grids-2) source (name of data provider) count (max number of sightings for the species for that day and site