The pictures on this post were all taken with my phone, so apologies for a little fuzziness!
Last year, much to my wife’s annoyance, I found a number of Small White caterpillars feeding on some Rocket plants that she was growing. As they grew larger and started to destroy the plant, I put the pot in a mesh butterfly cage and fed the caterpillars with cauliflower leaves.
The caterpillars grew quickly and started forming
chrysalises around the cage and under the rim of the plant pot saucer.
A couple of days before they form a chrysalis they choose a spot and weave a small silk pad. They then hook themselves to the pad and loop another length of thread like a girdle around themselves.
The caterpillar then thickens over the next couple of days and sheds its skin one final time. The chrysalis then forms over the next few hours. The picture below shows a newly formed chrysalis.
I kept an eye on them and at the end of October I noticed
one of the chrysalises had started to colour up. Normally, this is something I
see about four days before a butterfly emerges. As they reach the final stages
of development the pattern on the underside of the wings becomes apparent
through the wall of the chrysalis. I had always thought that once this final
stage of development had started, there was no stopping it. So, I was expecting
to see a very late third generation Small White, but the weather took a turn for
the worse and the butterfly did not emerge.
I periodically checked the chrysalises over the winter and
this April when I turned the saucer over I saw that the butterfly had started
to emerge, but must have become stuck half way out and it had perished. Although
this was sad for this individual, it proved that a chrysalis is able to survive
for six months over the winter at this late stage of development.
Between the 25th April and the 28th May 29 Small White butterflies emerged from the 38 chrysalises around the cage. 22 of them were females and only 7 were males.
Seven of the chrysalises turned black or brown over winter and failed to develop. However, there is one in the cage that still looks as though it could be OK.
