Swallowtail Butterfly (Papilio machaon)

InsectButterflyLepidoptera

Overview

The Old World swallowtail (Papilio machaon) is a large, striking butterfly of Europe, Asia, North Africa and parts of North America. It is pale yellow with bold black veining and margins, blue lunules and a red eyespot on the hindwing, which is drawn out into the pointed tail that gives the group its name.

It belongs to the family Papilionidae, the swallowtails — a group of large, often spectacular butterflies found worldwide.

Its most distinctive feature is not on the adult but on the caterpillar. When threatened, a swallowtail larva everts a bright orange forked organ from behind its head — the osmeterium — which releases a strong smell and startles or repels attackers.

Habitat & Range

The Old World swallowtail is widespread across Europe, temperate Asia and North Africa, with populations in North America. It uses open, flowery habitats — meadows, grassland, hillsides, marshes and fens — wherever its larval host plants grow. In Britain the species is confined to fenland where its single host plant, milk-parsley, survives, which makes that population far more restricted than the species as a whole.

Diet

Adults feed on nectar from a range of flowers, and are strong fliers that visit widely scattered blooms. Caterpillars feed on plants in the carrot family, Apiaceae — fennel, wild carrot, milk-parsley and relatives — and in some regions on rue. Host plant choice varies between populations, and the specificity of that choice is what constrains the butterfly's distribution.

Behavior

Males often perform hilltopping, gathering on high ground where they patrol and wait for females — a mate-locating strategy used by a number of butterflies. Caterpillars pass through dramatic changes: early instars resemble bird droppings, an effective disguise, before becoming the familiar green larva banded with black and marked with orange spots. The osmeterium is deployed only under threat. The species overwinters as a pupa attached to vegetation.

Human Interaction & Conservation

Swallowtails are among the most admired butterflies and are widely used as flagship species in insect conservation. Their dependence on specific host plants makes them sensitive to habitat change: the British population, restricted to fens where milk-parsley grows, is a clear example of how a widespread species can be highly vulnerable at the edge of its range. Habitat management for the host plant is the central conservation measure. Status varies regionally; verify at the IUCN Red List.