- Lifespan
- 2–6 weeks as an adult butterfly; complete life cycle from egg to adult takes approximately 4–6 weeks depending on temperature
- Size & Weight
- Wingspan 64–100 mm; one of the UK's largest native butterflies
- Habitat
- Open, sunny areas with fenland, marshland, and coastal habitats where milk parsley and other umbelliferous plants grow.
- UK Distribution
- Restricted to Norfolk and a few other East Anglian fens; formerly more widespread across southern England. Resident population with occasional continental migrants in summer.
- Diet
- Adults feed on nectar from teasels, thistles, marjoram, and other flowering plants; caterpillars feed exclusively on umbellifers, particularly milk parsley, fennel, and wild carrot.
- Predators
- Birds (particularly robins and wrens), spiders, parasitic wasps, and ground predators of caterpillars and pupae
- Mating Season
- May to August, typically in two broods per year
- Breeding
- Females lay single eggs on food plants; caterpillars take 2–3 weeks to develop; pupation occurs either as a chrysalis that overwinters or develops into a second brood within 1–2 weeks
- Behaviour
- Swallowtails are powerful, rapid fliers with characteristic gliding flight; males patrol territories and perch on vegetation in warm sunshine. They are highly territorial and males engage in aerial contests. The species is notably sensitive to habitat disturbance and requires specific wetland conditions.