European Swallowtail (Papilio machaon) – Complete Care Guide

Papilio machaon is one of the most iconic and rewarding swallowtails to rear. With fast caterpillar development, distinctive instars, and striking butterflies, it offers a fascinating rearing experience for both beginners and experienced keepers.

Egg Care

Swallowtail eggs are more sensitive to humidity changes than many other butterfly species.

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How to care for eggs

  • Keep eggs in a closed plastic container to prevent drying out.
  • Avoid direct sunlight.
  • Eggs begin pale yellow/cream, then darken shortly before hatching.
  • Hatching occurs within a few days, as the egg stage is brief (usually less than a week during warm weather).

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Important note

Do not add leaves before hatching. Fresh leaves release moisture, which can cause mould and kill the eggs before the caterpillars emerge.

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European Swallowtail caterpillars in L3

In the first couple of stages of life, European Swallowtails resemble bird droppings - an excellent disguise to avoid the attention of predators like birds! - before becoming more colourful in the later stages.

Host Plants for Papilio machaon

While many swallowtail species use Rutaceae, Papilio machaon uses Apiaceae (Umbellifers) as its primary host plants.

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Best host plant (strongly recommended):

  • Fennel (Foeniculum vulgare)
  • Garden Rue (Ruta graveolens)

P. machaon larvae grow exceptionally well on fennel and show strong feeding preference for it.

Other accepted host plants:

  • Carrot
  • Parsnip
  • Dill
  • Parsley
  • Wild species of Umbellifers (e.g., wild carrot)

These plants are easy to grow, widely available in the UK, and make acceptable host options for rearing indoors or outdoors, but may not produce as reliable results as Fennel.

Caterpillar Care

Once the larvae hatch they should be moved to a separate container with fresh host plants. When they are in the second instar and feeding reliably:

  • Move them to mesh cages for best airflow - Poor ventilation and stagnant air can cause rapid disease spread in young larvae of this species.
  • Using living potted host plants is recommended but not completely necessary if you can keep foliage fresh in jars of water. Caterpillars thrive on natural, growing foliage and cut Fennel can wilt quite quickly.

Different Stages of Development

In the final stages, caterpillars become large and very colourful!

Caterpillar Growth & Behaviour

Swallowtail caterpillars have distinctive developmental stages:

  • Early instars resemble bird droppings, providing natural camouflage.
  • Later instars become green with banding, typical of Papilio machaon.
  • When disturbed, they may extend the osmeterium, a forked, orange defensive gland with a noticeable scent.

    This behaviour is harmless to humans and rarely triggered in captivity.

    Caterpillars grow quickly and usually reach pupation around week 3-4 if temperatures are warm.
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Papilio machaon Pupae

Healthy pupae are quite chunky and can be either green or brown in colour. There may be more brown pupae in the overwintering brood, but the colour does not necessarily predict diapause.

Pupation (Chrysalis Stage)

When ready to pupate, Papilio machaon caterpillars:

  • Secure themselves to a stem or enclosure wall
  • Create a silk sling to hold themselves upright
  • Transform into a chrysalis after a few days


How to care for pupae

  • Leave pupae in situ whenever possible—no need to move them if you have reared yourself.
  • Maintain room temperature and moderate humidity.
  • Light daily misting prevents desiccation, especially in centrally heated or air conditioned homes.
  • Purchased pupae that arrive by post should be maintained according to our guide for pupae and cocoons.


Emergence timing

  • Pupae formed April–August usually emerge the same season (2–4 weeks).
  • Pupae formed September–October often overwinter until spring.

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Overwintering Papilio machaon Pupae

If overwintering occurs:

Safe storage options

  • Closed plastic container in the fridge
  • Protects pupae from temperature variation that can cause early emergence or development issues
  • Must remain closed: most fridges dehumidify and will dry out pupae


  • Cool outhouse, shed or porch
  • Store in a ventilated tin or container
  • Natural winter temperatures work well

Avoid freezing or overly warm conditions.

Adult Butterfly Care

Adult Papilio machaon are easy to maintain and can be cared for as outlined in our Adult Butterfly Care Guide. They require:

  • Ample space for flight
  • A stable, bright and warm environment during the day
  • Access to nectar or sugar-water - they will usually require hand-feeding
  • Suitable perches for resting and wing-drying

The adult stage is highly rewarding, and individuals may display subtle differences in colour - ranging from a pale cream colour to yellow. Interestingly, they can also successfully hybridise with closely related butterflies like Papilio polyxenes.