The Old World swallowtail butterfly has yellow wings with black vein markings and large spots. The hind wings have a wide band of blue with an orange-red eye spot at the lower angle. The hind wings also have protruding tails of up to 1 centimetre in length which give the butterfly its common name. Adults have a wingspan of up to 8.5 centimetres. The caterpillars are large and generally green with black rings that are dotted with orange, yellow or red. The caterpillar feeds on wild dill, fennel and other umbellifers. The pupae are green or reddish brown.
The swallowtail lives in warm habitats and prefers damp places were its favourite food plants can be found. In forest habitats, the butterflies are typically found in meadows and clearings and along riverbanks. They are also quite common in agricultural landscapes.
The Old World swallowtail can be seen in flight between May and June and from July to August. It has a strong, fast flight but frequently hovers over flowering herbs to sip nectar.