A shimmer of blue, something highly likely in case of a chrysalis that belongs to a Blue and is about to hatch. However, with Blue’s the determination of the species is often tricky. Here’s just another case where I was completely wrong until the very end.
Earlier this year I found two caterpillars of Blues. I expected the caterpillars to be of the Mazarine Blue (Plebeius semiargus). But what eventually hatched was a female Common Blue (Polyommatus icarus). In this case I luckily took one of the caterpillars home. This specifically to be able to get confirmation on the species. Unfortunately, I only took one of the larvae. To be absolutely sure both were the same species I’d have had to raise each of them.