The Anise Swallowtail, Papilio zelicaon, is a common swallowtail butterfly of western North America. Both the upper and lower sides of its wings are black, but the upper wing has a broad yellow stripe across it, which gives the butterfly an overall yellow appearance. There are striking blue spots on the rear edge of the rear wing, and the characteristic tails of the swallowtails. Its wingspan is 7-9 cm. Its body is somewhat shorter than the rather similar Western Tiger Swallowtail, with which its range overlaps; it also lacks the black stripes, converging towards the tail, of the latter. There is a somewhat darker subspecies, Papilio zelicaon nitra, which is rare throughout the range, though somewhat more often found at lower elevations.

The Anise Swallowtail is a butterfly of fairly open country, and is most likely to be seen on bare hills or mountains, in fields or at the roadside. It is often seen in towns, in gardens or vacant lots.

The caterpillar is green, with dark bands spotted with yellow. Its major food plants are members of the carrot family, Apiaceae, (including fennel), and also some members of the citrus family, Rutaceae. Like all swallowtail caterpillars, if disturbed, it will suddenly sprout bright orange osmateria or "stinkhorns" from just behind its head, which give off a foul odor. The caterpillar grows to around 5cm in length before forming a chrysalis, which is brown or green in colour and about 3cm long.

The normal range of the Anise Swallowtail extends from British Columbia and North Dakota at its northern extreme, south to Baja California and other parts of United States, but its normal range does not extend east of New Mexico, and even in the south-western states it is uncommon in the desert regions. In the southern parts of its range, the adults can be seen year-round, but in the north-west coastal regions, there are two flights, in spring and fall, while in the coldest parts of its range, there is a single flight, between April and July. In all the more northerly parts of the range, the chrysalis hibernates.