IMIS

Generalized and/or withheld information: location information is generalized to 5 x 5 km² Universal Transverse Mercator (UTM) grid cells. Observer name, exact XY-coordinates, toponyms, and photographs are not included in the published dataset, but are known in the source database.
Geographic coverage: Flanders and the Brussels Capital Region. These regions are situated in the north of Belgium and cover an area of 13,522 km² and 162 km² respectively (13,684 km² in total or 45% of the Belgian territory). Flanders is largely covered by agricultural land and urban areas while the Brussels Capital Region is mainly urban. All occurrence data are generalized to grid cells of 5 x 5 km² of the Universal Transverse Mercator (UTM) coordinate system, with the grid codes indicated in the field verbatimCoordinates. The WGS84 centroids of these grid cells are calculated in decimalLatitude/Longitude with a coordinateUncertaintyInMeters of 3,769 meters using Wieczorek et al. 2004.
Taxonomic coverage: The dataset covers 49 of the 68 native as well as 3 regular migrant butterfly species (Colias croceus, C. hyale, and Vanessa cardui). Aporia crataegi, Argynnis adippe, Argynnis aglaja, Boloria selene, and Coenonympha tullia no longer have breeding populations in Flanders and recent observations are all considered as vagrant individuals in this dataset. 10 vagrant species with photographic evidence, that most likely spontaneously reached Flanders (Apatura ilia, Brenthis daphne, Brenthis ino, Cupido argiades, Iphiclides podalirius, Lampides boeticus, Nymphalis xanthomelas, Pieris mannii, Polyommatus coridon and Pontia daplidice), are also included. Two observations from Danaus plexippus are most likely escapes but the origin could not be confirmed. If the observer remarked that the specific individual was introduced by man, then this is recorded in the field establishmentMeans.
Sampling methods: The observations (species, date, location, observer) were recorded by volunteers (citizen scientists) at http://www.waarnemingen.be.
Quality control: Recorded data are constantly verified by butterfly experts (including professional entomologists) taking collection specimens, the observer’s species knowledge, added photographs and known species list of locations into account. The validation procedure from waarnemingen.be consists of an interactive procedure in which observers can be asked for additional information by a team of validators, after which the validator manually adds a validation status. Records that are not manually validated are additionally checked by an automated validation procedure that takes into account the number of manually validated observations within a specified date and distance range. 10% of the observations in this dataset are supported by a photograph on waarnemingen.be. The validation status is indicated in the field identificationVerificationStatus, the link to the original record in references.
Purpose: Butterflies are among the best studied insects in the world and have always attracted the attention of both professional researchers, amateur naturalists, butterfly collectors, and the wider public (Kühn et al. 2008). Butterflies are widely considered as interesting study systems for ecology, evolution, behaviour, and conservation biology (e.g., Watt and Boggs 2003). Many butterflies have been collected and subsequently stored in museum or private collections. Furthermore, entomologists have often published lists of observed species during excursions to special habitats or have made overviews of regional or national butterfly faunas. In Belgium, entomology in general and lepidopterology in particular, have a long tradition with the first faunas already published only seven years after its independence in 1830 (De Selys-Longchamps 1837). Since then, several authors have updated the Belgian butterfly fauna based on collections or observations (e.g., Hackray et al. 1969; De Prins 1998). In 1991, the youth and nature organization Jeugdbond voor Natuur en Milieu (JNM) launched a butterfly project with the aim to publish a distribution atlas of the butterflies of Flanders, north Belgium (Daniëls 1991). To do so, a first step consisted of collecting all historical collection and literature data. Secondly, a working group was organised in cooperation between JNM, De Wielewaal (which later became Natuurpunt) and the INBO that set up a citizen science project to obtain as many butterfly observations with a good spatial coverage over Flanders. The data gathered during this project (period 1991-1998) were used to compile a first Red List (Maes and Van Dyck 1996) and a distribution atlas of butterflies in Flanders, including the Brussels Capital Region (Maes and Van Dyck 1999). Recently, both the Red List (Maes et al. 2012) and the distribution atlas (Maes et al. 2013) were updated using recent distribution data recorded through www.waarnemingen.be, a data portal launched by Natuurpunt, the largest nature conservation NGO in Belgium, where citizen-scientists can store and keep track of their recordings. Here, we publish both the historical and the more recent data used for the Red List and the distribution atlases as a data paper on a UTM grid cell resolution of 5 x 5 km².
The publication of this dataset was supported by the INBO as part of the Flemish contribution to LifeWatch.