Swallowtail Butterfly Papilio machaon britannicus

Swallowtail butterflies are large, colorful butterflies that form the family Papilionidae. Swallowtails differ from all other butterflies in a number of anatomical traits. Most notably, their caterpillars possess a unique organ behind their heads, called the osmeterium. Normally hidden, this forked structure can be everted when the caterpillar is threatened, and emits smelly secretions containing terpenes. The adults are often tailed like the forked tail of some swallows, giving the insect its name.

Conservation status in Norfolk

During the 20th century, especially after the Second World War, fenland management ceased and much of this butterfly’s habitat was lost. Today active management of the fenland, where reed and sedge are cut to allow other plants to grow, plays an important part in the survival of the swallowtail in Norfolk. With this continued fenland management, the future for the swallowtail looks brighter.

Click to see the Biodiversity Action Plan Species for this species

How to help

Create a butterfly-friendly garden full of nectar-rich flowers. You never know – if you live near the broads you may encourage a swallowtail to visit your garden.

Adopt me today and help ensure my future!

Craig Shaw

Information on the Swallowtail Butterfly

How to recognise

Britain’s largest butterfly, the swallowtail, has a wingspan of up to 9cm and has stunning yellow and black markings. It takes its name from its two long tail extensions which resemble a swallow’s tail. The caterpillars begin life resembling black and white bird droppings, but as they grow, they become plump bright green caterpillars 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.

Where to see

The swallowtail butterfly is now limited to the Norfolk Broads choosing sites with a vigorous growth of milk parsley, where it lays its eggs on the tallest plants. Although a rare British insect, if you go to the right place, such as NWT Hickling Broad, NWT Ranworth Broad or RSPB Strumpshaw Fen, at the right time, early morning on a bright summer’s day, then with luck you will spot one.

When to see

The swallowtail spends the winter hibernating as a pupae at the bottom of a plant stem, where they can withstand being submerged in water for long periods. 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.

Did you know?

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.

Finding out more

Norfolk & Norwich Naturalist Society

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