<p>Butterflies and moths have often been suggested as suitable indicators for monitoring environmental effects on biodiversity, land use changes and management practices, and many butterfly monitoring schemes are established and run in Europe. In these monitoring programmes, the field counts are only carried out when certain, standard weather conditions considered favourable for butterflies are met. Here, we tested if the prescribed standard weather conditions are suitable across bio-geographic regions, or if the given variance of the weather conditions would still cause effects on monitoring results of butterflies. In addition, we examined how flower density alongside butterfly transects affected the recorded abundance and species number. We operated linear 1-km transect routes in Romania, Spain and Sweden from 2013 to 2015, and recorded butterflies and burnet moths (Papilionoidea, Zygaenidae). The transects were walked back and forth four times per season, and replicated yearly. The following parameters were measured and analysed for their effect on butterfly abundance and species number: country, date and time, temperature, wind speed, sunshine percentage and flower density. In general, weather conditions within the specified range did not cause high variance in recorded butterfly abundance and species richness. In contrast, flower density had a strong impact on butterfly abundance in Sweden and Spain, but less so in Romania. In conclusion, the standard weather conditions imposed and applied in European butterfly monitoring schemes appeared appropriate, for three different bio-geographical and climatic regions across Europe. However, flower density was identified as an important factor affecting butterfly abundance, and is suggested to be routinely recorded as a variable in butterfly monitoring schemes.</p>