[1] Swallowtails have a number of distinctive features; for example, the papilionid caterpillar bears a repugnatorial organ called the osmeterium on its prothorax.

The osmeterium normally remains hidden, but when threatened, the larva turns it outward through a transverse dorsal groove by inflating it with fluid.

In swallowtails, besides morphological characteristics, the choice of food plants and ecological lifestyle reflect phylogeny and classification.

Baronia brevicornis is considered to be a relict species, and shares features with a fossil taxon Praepapilio.

Parnassiinines can also be found in other habitats such as "arid deserts (Hypermnestra), humid forests (Luehdorfia) and even lowland meadows (Zerynthia)".

Tribe Parnassiini contains two genera, Hypermnestra, largely confined to central Asia and the genus Parnassius (the Apollos), a distinctive group of many species, all of which are alpine and capable of living at high altitudes.

[8] A phylogeny of the Papilionidae based on Nazari (2007) is given:[1][7] (†) Praepapilioninae Baroniinae Parnassiini Zerynthiini Luehdorfiini Leptocircini Teinopalpini Papilionini Troidini It is now accepted that the subfamily Papilioninae is monophyletic.

[1] The swallowtail butterflies in the nominate tribe Papilionini number about 225 species and studies have been made on their host plant coevolution and phylogeny.

[1] Of the Parnassiinae, the genera Parnassius and Hypermnestra were found to be extremely close based on molecular studies[10] and are now considered to be part of the tribe Parnassiini.

[7] The two taxa, Archon and Luehdorfia, have been found to be closely related through analysis of nuclear and mitochondrial DNA, and, though they share no morphological similarities, have now been united in the tribe Luehdorfiini.

Recent research suggests that this may not be the case, the Baroniinae being closely related to only the Parnassiinae, and Praepapilio to only the Papilionini and neither taxa being sister to the rest of the swallowtails.

[13] The northernmost swallowtail is the Siberian Apollo (Parnassius arcticus), found in the Arctic Circle in northeastern Yakutia, at altitudes of 1500 meters above sea level.

[14] In the Himalayas, various Apollo species such as Parnassius epaphus, have been found at altitudes of 6,000 meters above sea level.

[15]: 221 The caterpillars of various swallowtail butterfly species feed on a wide range of different plants, most depending on only one of five families: Aristolochiaceae, Annonaceae, Lauraceae, Umbelliferae (Apiaceae) and Rutaceae.

[16] Similarly, the Parnassius smintheus sequesters sarmentosin from its host plant Sedum lanceolatum for protection from predators.

The second segment has a transverse opening, out of which the larva protrudes at will and an erect, forked, glandular fleshy organ that emits a strong, penetrating, and somewhat unpleasant odor.

[22] Predators include the red-winged blackbird, Pennsylvania firefly, five-lined skink, green darner, goldenrod spider, Chinese mantis, fiery searcher, and striped skunk.

The enzyme BAS, which assists dopamine in producing the yellow pigmentation, normally found on the wings' background, is suppressed.

Without the pigmentation, the butterfly appears mostly black (the melanic form) and is a Batesian mimic of Battus philenor, the pipevine swallowtail.

Studies support this theory; in the southeastern United States, the relative abundance of melanic females has been found to geographically correlate with B. philenor.

[24] The scientists concluded that frequency-dependent selection did lead to equal success for all three alternative strategies: the Batesian females suffered the fewest predators but their fitness was reduced the most by sexual harassment, while the other two faced lower sexual harassment but also lost fitness from predators' attacks.