A Butterfly’s Data

It turns out that some people visiting our website are actually looking for data about butterflies, which up until now we were sadly unable to provide - here we rectify that! There are over 18,500 species of butterflies worldwide and every continent, except Antarctica, has its own beautiful examples. Their life cycle involves four distinct stages: egg, caterpillar, chrysalis and finally butterfly. Many are endangered species, due to loss of habitat, increased use of pesticides, and warmer weather.

Here in Britain there is an annual Big Butterfly Count which has been running for 13 years. There has been a general decline in numbers recorded, but within this there are winners and losers from one year to the next causing a change in the geographic distribution - for example the Holly Blue has extended its range northwards across Scotland. It is the largest citizen-science project of its kind and relies on volunteers across the UK, results are then broken down by country. Many countries around the world have initiated their own butterfly counts and databases, including India and Australia, where species have been identified which had previously only been spotted in south east Asia.

In North America the Monarch butterflies pictured below are capable of traveling 50 to 100 miles per day in one of the most spectacular migrations of the natural world. The world wildlife fund has been tracking the population of these migrations since 1995, not by counting individual butterflies arriving in the Monarch Butterfly Biosphere Reserve in Mexico, but by measuring the area of forest occupied by the population. There had been a steady decline from 45 acres in 1995-6, to 27.5 acres in 2003-04 and just 5 acres in 2020, but the figures for 2021 had rebounded slightly to 7 acres. These figures are in line with similar counting exercises in California - the Xerces Society for Invertebrate Conservation hold an annual Thanksgiving count and have recorded a 99.4% decline since the 1980s.

Coordinated data collection and analysis is the only way to determine whether interventions such as banning certain pesticides will work, so this is yet another example of data potentially supporting evidence-based policy to reduce environmental harms.