[Alice]

This butterfly on Ballota acetabulosa (?) was seen in a very dry habitat. What is it?

[MikeHardman]

Good photo, Alice.

It is a relative of the marbled white (Melanargia galathea) some UK folks will be familiar with. That also occurs in Greece (N. & C. parts), where it is common and widespread in woodlands (in the UK it prefers open downland).
Your one is Melanargia larissa, Balkan marbled white, which is common and widespread in Greece. It has a subspecies, endemic to Lesbos - M. l. ssp. lesbina.
It is distributed from Spain to Greece. In France and Spain it occurs as ssp. cleanthe; in Italy and Greece as ssp. japygia, which has heavier markings.

(There is also M. russiae, Esper's marbled white, which looks very similar to M. larissa, but in Greece it is confined to the NW., where it occurs locally above 1,600 m. There are a few other species of Melangaria in other parts of Europe, and more from northern Africa to central Asia.)

Note: the common names Balkan marbled white and Esper's marbled white are often mixed-up, ie. used for each other's species. I have used the more common associations of names to species.

Refs:
- http://users.auth.gr/~efthymia/Butterflies/larissa.html
- http://users.auth.gr/~efthymia/Butterflies/russiae.html
- http://users.auth.gr/~efthymia/Butterflies/Butterflies_of_Greece.html
- http://www.leps.it/indexjs.htm?SpeciesPages/MelanRussi.htm
- http://www.eurobutterflies.com/species_pages/russiae.htm
- http://en.wikipedia.org/wiki/Melanargia

[Alice]

Many thanks, Mike. Interesting websites. I see that Melanargia larval host plants are grasses, however eggs are not laid directly on them but sprinkled above them in mid-air.

[MikeHardman]

Yes Alice.
Marbled whites are more closely related to browns than whites. The browns are specialist grass feeders (as larvae). Presumably there is some benefit to sprinkling eggs as they fly. It must make the adults less likely to get ensnared in cobwebs or caught by mantids; and it must use less energy per egg.