... as adults a fortnight later, after twelve to seventy-two hours as pupae. This is summarised in Figure 1. As the larva hatches out of the egg, it's sole purpose is to feed so that it has enough energy for the metamorphosis during the non-feeding pupal stage. At the larval stage, a developing bluebottle has no protection from radiation, and it's white skin would make it stand out strongly to predators. Later towards the pupal stage it develops protective pigment, and changes to a less conspicuous brown colour. As the eggs are laid in a foodstuff, it is only natural that it would be beneficial to the larva to stay there in the nutrient-rich, insulated, moist, and predator-free environment until it has enough energy and it pupates, and develops into a fly, when it requires to be in the open. It has, needless to say (nature is almost always perfect), evolved ...

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