a basic, probably dumb question I haven't found the answer to yet.

[Ernest Williams]

Just to add to Niklas' comments - for oviposition, scent can help females
find the right plants.  Volatiles enhance landing rates in _Papilio
polyxenes_, the Black Swallowtail (North Amer.). (Feeny et al., 1989, J.
Insect Behav. 2:803-827)

Ernest Williams

>
>...Ovipositing females however appear to be attracted by
>leaf shape. This has been shown for one species of swallowtail (Battus
>philenor if I remember correctly). The melitaeines that I have studied also
>prefer to land on plant species with similar leaf shape to their host plant
>when ovipositing, though I haven't tested this rigorously. Once they have
>landed, they taste the plant to identify it.
>
>Cheers,
>Niklas