Colias palaeno (Linnaeus, 1761)

Host plants:
The caterpillars feed on Vaccinium uliginosum.

Habitat:
Colias palaeno inhabits on the one hand bogs and moorlands in lower altitudes and on the other hand siliceous areas in high mountains: dry to wet alpine meadows and especially the dwarf shrub belt.

Life cycle:
The adults fly in June and July (in cold regions like high mountains sometimes still in August) and lay eggs on the bilberry leaf upper side. Oviposition takes place especially on sunny and mostly small, marginal shrubs. The young larvae feed on the upper leaf surface (characteristic feeding pattern: scraping of the upper surface). They rest mostly on the upper side of the leaf base on a silken seat pad. Hibernation takes place in the third instar at the lower side of a leaf on a seat pad. This position is already assumed in August or at the latest in September. This hibernation leaf usually falls to the ground into the litter/moss in autumn. The larva moves not until spring. In April, the larvae ascend to the plants again and can be easily detected for example by tapping. Pupation takes place in late May on branches of the host plant or nearby other stalks, etc.

Endangerment factors:
As an inhabitant of bogs Colias palaeno is threatened with extinction. Nowadays, only tiny remnants of the once vast bogs are present in central Europe, and these have in most cases a disturbed water balance. Additionally there are the eutrophication from the air (pollution), climate change and the conversion of the bog environment (agricultural intensification or afforestation). Especially afforestation of moorland edge areas with spruce, but also their transformation into intensive manure meadows deprive the butterflies of the food sources because the bog core - the larval habitat - is poor in flowers. Colias palaeno shows with drainage and disturbance initially a significant increasement in numbers because now more blooms and Vaccinium bushes are available. But then the shrubs grow tall (up to 1 meter) and are finally overgrown by birch or pine succession scrub and Colias palaeno dies out quickly. The same can be observed in some grasslands species after the abandonment of grazing.
Today, there are additionally effects of global warming. Colias palaeno is adjusted to cold winters and especially in low altitudes many larvae perish during the more and more wet and warm winters (fungi).

Remarks:
The total distribution ranges from central and northern Europe across northern Asia to Japan. Beyond this, Colias palaeno is also found in the Nearctic. In N-Europe occurs the pale white nominate form, in central Europe the yellow europome.
In the Alps - in particular the central Alps, but hardly in the Bavarian Alps - Colias palaeno is more widespread in the dwarf shrub zones (Rhododendro-Vaccinietum).