BMS - methods



Butterflies, in common with some other groups of insects, have declined in many places in recent decades. We need their monitoring to understand the causes of decline and to support conservation measures. We can get useful information and important results with butterfly monitoring by citizen science. 

You could help us counting butterflies with different methodologies depending on your preferences. Butterflies can be monitored by anyone who has the time and is willing to learn the butterfly species from their place. There are hundreds of methods to count butterflies but not all of them provide the same information. In this page we will explain the two groups of data, Opportunistic Data and Monitored Data: 




Opportunistic Data

It is only required the coordinates and the species name, usually taking pictures. This type of data are normally used for citizen science websites to collect big amount of data from volunteers/amateurs such as iNaturalist, Obersavdo, GBIF, eBird… It is a simple method uses in large numbers useful to know the species distribution area. With opportunistic data, we can know which species are in one area and how the species move throughout the space.  

                              -    You need a camera or smartphone

                              -    Have an interest in nature and environment

                              -    Low time invested

With a small amount of effort opportunistic data gives useful information about species but it is not possible to know the abundances (how many individuals of one species?). It is more complicated to answer this question with the Opportunistic Data methodology.both

Some online resources:

  • iNaturalis You can create an account and use it on the website or in the App. Useful tool that help you to identify species. You take the picture and make a suggestions of the possible species, so it could be so useful for beginners to start with the identification of butterflies!


  • Observado Website and App where you can upload observations without pictures. There is a filter to accept the record based on former observations and there are experts checking pictures. However, it is always better to say the species name or at least the butterfly genius or butterfly group (Rhopalocera)



Monitored data

This type of data involved a bit more of monitoring effort but it provides incredible information for the science (species abundances). Ecologists use this type of method (investing more time) to collect proper data. Monitored data is important and necessary to know the population trends of our species: if we want to know if one specific species is growing or decreasing in numbers, we need to use this type of methodology.


  • You would need to identify the butterfly species name
  • Commit with nature and nature conservation
  • Invest a bit more time than with opportunistic data (just a bit more!)

There are different types of monitored data where the time and standardised methodology is involved depending on the information that you want to get. Methods for butterflies are like the egg counts in the habitat species, Malaise trap, light traps (months), time counts or transects. Here we will explain the two methods that we used in eBMS:



Transect Counts - Pollard Walks

A transect is a fixed route (walk) established at a site where butterflies are recorded, weekly, over a number of years following some basic rules. The majority of transects are chosen by the walker and they decide which route to choose. Some schemes provide advice about areas to record to get even coverage of land cover/ habitat types as well as ensuring that a good range of the species present in a country are sufficiently monitored.

You can do the counts as part of a team: it is more fun to share experiences of what you saw and you can replace each other during holidays. There is just a few rules to follow for doing a transect:transects

  1. Transects are typically about 1km long and divided into sections that correspond to different habitat areas, or are a fixed length (e.g. 50m).
  2. Butterflies are counted when adults are present - e.g. during the flight period of butterflies. Depending on the country and the region, the flight period of butterflies will be longer or shorter. 
  3. The transect is ideally walked every week during the butterfly flight season. If it is not possible, count as often as possible, every two weeks or 10 days. Don't leave more than 3 weeks between one visit and another.
  4. Count butterfly adults in an imaginary box of 2.5m to each side, 5m high and 5m ahead. 
  5. The visits should be done with good weather: sunny and warm, with no rain and not too windy.



Timed Counts 

This type of monitoring is used to obtain butterfly abundances and it has been used for monitoring rare species and butterflies with specific behaviors. This method is basically based on monitoring in an specific area for a fixed amount of time, in eBMS is 15 minutes. We recommend this type of method for people with quite knowledge in butterfly that like to visit different areas and habitats. 

Keeping the same time in areas with similar extension, it will produce standardised results which you can obtain butterfly abundances. This method is used for butterflies such as Mellicta athalia and Argynnis adippe in the United Kingdom. 










More information

If you want to have more information of these methodologies, please refer to the Manual for Butterfly Monitoring and the Butterfly Transect Counts Manual. There may be other methods used for butterfly monitoring. For studies on specific species or populations it may be necessary to adopt more complex methods. Please refer to the list of references below to find more information about other techniques used for butterfly monitoring. 









Nowicki, P., Settele, J., Henry, P. Y., & Woyciechowski, M. (2008). Butterfly monitoring methods: the ideal and the real world. Israel Journal of Ecology and Evolution54(1), 69-88.
Van Swaay, C., Regan, E., Ling, M., Bozhinovska, E., Fernandez, M., Marini-Filho, O.J., Huertas, B., Phon, C.-K., K”orösi, A., Meerman, J., Pe’er, G., Uehara-Prado, M., Sáfián, S., Sam, L., Shuey, J., Taron, D., Terblanche, R., and Underhill, L. (2015). Guidelines for Standardised Global Butterfly Monitoring. Group on Earth Observations Biodiversity Observation Network, Leipzig, Germany.
GEO BON Technical Series 1, 32pp.
Van Swaay, C.A.M., Brereton, T., Kirkland, P. and Warren, M.S. (2012) Manual for Butterfly Monitoring. Report VS2012.010, De Vlinderstichting/Dutch Butterfly Conservation, Butterfly Conservation UK & Butterfly Conservation Europe, Wageningen.
van Swaay, C. A., Nowicki, P., Settele, J., & van Strien, A. J. (2008). Butterfly monitoring in Europe: methods, applications and perspectives. Biodiversity and Conservation17(14), 3455-3469.