In autumn 2020, two plot holders reported discovering some amazing looking caterpillars happily munching away on plants on their plots. After a bit of research, it turned out that these caterpillars were in fact those of the Swallowtail Butterfly – one of our rarest and most spectacular butterflies, normally only found around the Norfolk Broads and in mainland Europe.
Giving nature a helping hand
To help his Swallowtail caterpillars reach adulthood, Stuart decided to bring the two caterpillars he saw indoors. Here he relates what he did:
“I found two Swallowtail butterfly caterpillars on some fennel on our Craven Vale allotment last October. I didn’t think they would survive the winter so decided to look after them until the Spring. Initially I put them on pieces of fennel in a white bucket as they were still feeding. The next stage was to introduce a couple of twigs to the bucket for them to attach to for when they were ready to change into a chrysalis, which they eventually did”.
“I then set up a home for them in a small butterfly tent in my allotment shed, to protect them from the worst of the winter. They overwintered there until May 2021 when I noticed one had changed to a darker colour. The next day it emerged as a beautiful Swallowtail butterfly. The moment I had been waiting for! – this was my very first view of a Swallowtail in the UK. The day it emerged was sunny with light winds so I felt happy releasing it.
The second chrysalis took another week to emerge and unfortunately the timing wasn’t great as the weather had taken a turn for the worse, being cold, windy and rainy. This went on for a few days and I started to worry about it surviving, as obviously it would need some form of food. The internet came to the rescue with information on force feeding. This sounds a terrible thing to do, but this was a do or die situation. So, I mixed up a solution of honey and water and put this in a shallow lid. The butterfly doesn’t know that this is food so it needs to be helped. I lightly held the butterfly with my thumb and forefinger with its wings closed, with the dish of honey mixture in front of it and gently unfurled its proboscis with a fine pointed tool, then dipped the proboscis in the fluid. To my surprise it worked, the butterfly started sucking up the liquid. For a few days I kept feeding twice a day until eventually the weather improved and I could release it. Poetically, it took off and soared up into the blue sky heading east towards the Downs until I could see it no more”.
If you have fennel on your plot, their food of choice, then keep a look out this autumn, you never know!
With big thanks to Craven Vale allotmenteer Stuart for his story and images.