Monitoring is important in order to evaluate the condition of a certain area in terms of species occurrence, species-richness and changes in abundance. The findings of this study show that monitoring of bumblebees can be performed over the whole day, independent of temperature, cloudiness and wind speed as long as the temperature is above 17 ˚C and the wind speed below five on Beaufort’s scale (fresh wind). The fact that bumblebees are so indifferent to weather conditions and not affected by time of the day make them easy to monitor in the field, which considerably facilitates survey and follow-ups on different bumblebee species and habitat conditions.

Power analyses were used to examine monitoring methodology. It is recommended that sites are visited at the beginning of the summer due to lower variation in bumblebee abundance. The number of bumblebees and species were found to be relatively stable between the middle of June and the middle of July and peaked at the beginning of August. The probability of detecting a certain change in abundance was not much affected by varying the number of visits, and as long as it occurs at the beginning of the summer it is sufficient with one visit per season. The number of sites, on the other hand, had a large effect on the probability of detecting changes in abundance. It was found that in order to detect a significant change in abundance, large scale monitoring with many visited sites is necessary. The calculations, however, are based on the assumption that samples are drawn from an infinite population and therefore the results are applicable on very large populations only, for example at national level. Generally, common species required fewer visited sites than less common species. To detect a 50% change in abundance of Bombus pascuorum, the most common species in this study, 295 sites must be monitored and for less common species, like B. pratorum and B. soroeensis, over 2000 sites must be monitored in order to detect a significant change in abundance.