Ruby tiger in Mõisaküla in Kiili parish. In the midst of a snow field a hairy caterpillar - "päevakoer“ or ”sun dog”. The snow crust is about 10 centimetres thick and can be walked on without sinking in.

Ruby tiger     Kevadkaruslane      Phragmatobia fuliginosa

The caterpillars of the ruby tiger are among the first sure spring heralds of the insect world each year. In thaw weather in winter we will not se them moving on the snow but already in early spring we meet them almost everywhere in nature: in meadows, on forest verges, clear cut forest areas …

The about 3 centimetres long ruby tiger is the most common of other similar caterpillars that can be seen on snow. These brown-furred caterpillars can be seen out walking on beautiful spring days in quite large numbers. How do these creatures manage in the winter cold and how come that the degrees of frost do  not kill them?

Now we must go back to last autumn when the caterpillars already were moving around. When the weather turned colder several changes took place in the cells of the larva: the intestines were emptied of food and water disappeared from the cells of the organism but was by and by replaced with glycerine that prevents the cells from freezing. They will be extremely resistant to cold because in laboratory conditions the caterpillars have been chilled down to 40 degrees of cold without damage.

The caterpillars may also be driven out on the snow to be exposed to the brilliant springtime sun by microfungi whose spores in the mild winter have found a favourable habitat in the fur of the ruby tiger. The UV light of the sunshine will destroy the fungi.

In addition to humans other ”furred and feathered” beings also notice the furry caterpillars openly on the white snow – they may seem to be quite tempting mouthfuls at a first glance? But birds for instance simply keep away from the bad-tasting caterpillars equipped with poisonous hairs.

Spring water is no particular problem for the caterpillars either, because their coat does not get wet and they stay floating on the water surface. Once I picked up such a creature from the water who looked quite sodden and set it at the puddle edge to dry – in a couple of hours  the hairs were dry and the caterpillar had its life spirit back. They are quite well prepared for life!

When the show has melted the ruby tiger caterpillars will quite soon pupate. The fully-grown adults or imagos start flying in May or June: small butterflies with dark brown wings, difficult to see in nature.