The swallowtail butterfly

Looking as though they have come straight out of the Amazon rainforest, our native swallowtail butterfly - Papilio machaon britannicus is an absolute stunner. It is our largest native butterfly with a wingspan approaching 10 cm, It takes its name from its two long tail extensions which resemble a swallow’s tail. Unfortunately it is also one of our rarest species.

Swallowtail butterfly -
Today, the swallowtail butterfly is now limited to the Norfolk Broads, preferring sites with a vigorous growth of milk parsley, where it will lay its eggs on the tallest plants.

The swallowtail will spend the winter hibernating as a pupae at the bottom of a plant stem. Surprisingly, they can withstand being submerged in water for long periods, a life saving adaptation for living in the Broads marshes and wet woodlands.

From late May, adults emerge and will live on average for one month breeding and feeding. The first brood of adults die by mid-July. Sometimes in August a second brood of adults emerge. These will lay eggs and their caterpillars will form pupae in September and hibernate over the winter.

Swallowtail butterfly caterpillar image credit -
Although a rare British insect, there are still reasonable populations at Hickling Broad, Ranworth Broad or Strumpshaw Fen. If you can make it out early enough on a bright summer’s day, with a bit of luck you will get to spot one.

The swallow-like tails of the swallowtail butterfly play an important part in the butterfly’s survival by mimicking antennae. These, plus two red and blue ‘false eyes’, confuse predators into thinking it is a two-headed butterfly.

To further aid its survival, their caterpillars begin life resembling black and white bird droppings! As they grow, the caterpillars turn bright green with black bands and orange spots along the body. If the caterpillar feels threatened, two horn-like bright orange scent glands emerge from the back of its head producing a smell, which has been likened to pineapple.

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