We’ve watched Brimstone courtship (Butterfly courtship, 24 May 2021) and we’ve seen Brimstone eggs (4 May 2021), now let’s have a look at what hatched out of those eggs, the Brimstone babies … well, we might want to call them caterpillars or, more scientifically correct, larvae, but I couldn’t resist the alliteration of that title.
According to Peter Eeles’s Life Cycles of British & Irish Butterflies, the Brimstone butterfly progresses through five stages, called instars, taking around 25 days from the day it hatches from its egg to the time it moults into its final instar. Six days after that, it pupates. By returning to Buckthorn trees where I’ve previously seen eggs, I’ve managed to find most of these stages, including, on Saturday, a final instar.
Eeles writes that, as early instars, the larvae tend ‘to rest alongside a rib on the leaf underside’ (shown in my first two photos) but from the third instar, ‘the larva now rests on the leaf upperside’ (above). In its final instar the larva has a typical resting pose, where it almost hangs off the leaf (below left), and it ‘exudes an amber liquid from the tips of the fine hairs that cover its body … This liquid may be distasteful to birds and therefore act as a deterrent’. The tiny orange globules can be seen in the photo below right. Now to find a pupa …