Chair of Hertfordshire and Middlesex Branch of Butterfly Conservation, Malcolm Hull shares his observations and findings from his garden shed on Small Tortoiseshell and Peacock butterflies. 

In recent years there have been concerns about the declining numbers of Small Tortoiseshell butterflies recorded in the Big Butterfly Count, particularly in the South East of England. In January BBC Winterwatch broadcast the results of my observations on Small Tortoiseshell hibernation, based on my observations of their behaviour from my garden shed in St Albans; a perfect environment for both Peacocks and Small Tortoiseshells to spend the winter months.

Previous years’ findings

  • During late June/early July Small Tortoiseshells begin to enter hibernation
  • In some years all Small Tortoiseshells appear to have entered hibernation by the end of July. In other years there is an additional trickle of second-generation individuals which enter hibernation up until the end of September.
  • In each of the last four years, a substantial majority of Small Tortoiseshells are in hibernation well before the end of the Big Butterfly Count in August
  • Once in hibernation, the Small Tortoiseshells very seldom wake up before Spring the next year

Small Tortoiseshell in hibernation, St Albans 24/06/20 photo by Malcolm Hull

What is happening in 2020?

  • Small Tortoiseshells began to emerge from hibernation in early March. The vast majority flew in two very warm weeks at the end of March and early April. This is slightly later than I’ve usually observed.
  • The warm weather in April and May helped the overwintering generation complete their breeding cycle quickly. The first of the summer generation of Small Tortoiseshells were on the wing in late May.
  • By the end of the third week of June they were beginning to demonstrate behaviours typical of the build up to hibernation. These include feeding all day on my garden flowers and exploring for hibernation spots by flying very slowly as if in first gear round the outside and inside of buildings.
  • Sure enough I recorded the first two hibernating Small Tortoiseshells on 24th June, the earliest ever date since I’ve been recording. This number slowly increased over the next four weeks and by the start of the Big Butterfly Count on 17th July there were six Small Tortoiseshells hibernating.
  • Why are they hibernating so early? My butterfly book says they hibernate at the end of summer, not the beginning! They are three months early and missing the best summer weather.

There are almost no Small Tortoiseshells flying in my area at the time of writing. But I am expecting a strong second generation this year which I hope will emerge during the Big Butterfly Count period.

Peacocks have also begun their hibernation in the shed early this year with the first three recorded on 22nd July. This is one day earlier in the year than the first hibernating records in 2018 and 2019, so perhaps this species is more consistent.

So what is going on? We know the behaviour of Small Tortoiseshell butterflies can vary a lot from year to year and. its behaviour in the South East of England appears to be quite different from other areas of the UK. Is this a response to climate change or other factors? Please keep sending in your sightings to Big Butterfly Count and if you are lucky enough to find hibernating Small Tortoiseshells or Peacocks, I’d love to hear from you. My contact email is @email

Malcolm Hull