Issoria lathonia (Linnaeus, 1758)

Host plants:
Viola spp. Viola arvensis is the usual host plant in arable fields, whereas it is often Viola hirta in grassland areas.

Habitat:
Issoria lathonia colonizes open land of all kinds, as long as larval host plants are available. It is particularly common in arable areas on limestone or sand. I observed oviposition in juniper grasslands on twigs and leaves on the ground as well as on the larval host plant Viola hirta and on fields on blades and Viola arvensis. In the Alps, Issoria lathonia rises up to 2500m above sea level, but is probably indigenous only to the Southern Alps. So I found a fully-grown caterpillar in 2300m above sea level on the Simplon Pass in Valais.

In Greece, I observed larvae on a debris site at a forest edge on Viola arvensis on Mount Olympus at 1000m above sea level in May 2010.

Life cycle:
Issoria lathonia is on the wing in several generations per year. The caterpillar overwinters mostly as L4 and is active again on the first sunny days in the early spring. I observed first butterflies in the Swabian Alb in April. Last adults of the alleged third generation can still be registered in late October.

Endangerment factors:
After a deep low point in the last decades Issoria lathonia became quite common in Central Europe in recent years and is likely to be at only little risk. Mainly the intensification of agriculture (over-fertilization, spraying, immediate furrowing) should limit the available habitat area severely.

Remarks:
The overall distribution ranges from North Africa across Europe and Asia to India and Mongolia.