Different animal species have developed different strategies when it comes to surviving the winter. Whilst some like the edible doormouse or bats hibernate for a long period, other species like squirrels or jays stockpile food. Wild boar can rummage through the soil even in subzero temperatures and, being omnivores, make use of almost everything they find. For roe deer, the high-energy buds of young trees in the forest are an important food source in winter. Insects survive the winter mostly in the transitional stages of pupa or egg, although some butterflies are so frost-hardy that they await spring simply hanging from a twig.