Mass ocurrence of the larvae of

Dasychira pudibunda in southern Sjælland

By  Jens Meulengracht-Madsen & P. Stadel Nielsen

The Lymantrid moth Calliteara pudibunda L. is widespread in Danish beech (Fagus sylvatica) forests. At rare occasions, populations suddenly and locally explodes and the caterpillers occurs in huge numbers. The species has one generation in Denmark, with the dull grey moth flying during June. Each female can lay 300-400 eggs which she normally does very near the place where she emerged from the pupae. The small caterpillar is very hairy and can easily be transported by the wind. In late autumn the caterpillar is fully grown, is about 5 cm long and is very beautifully coloured. Pupation takes place among leaves on the ground where a silken cocoon is made.

In the autumn 1998 a heavy attack of The Pale Tussock, Calliteara pudibunda L. was observed in Dyrlev Wood, a beech wood 10 km north of Vordingborg on the southern Zealand. The larvae defoliated particularly during August-September an area of 20 hectares of the wood. As it can be seen from the illustrations, a very great amount of the larvae had to starve and struggle themselves to death in their effort to get enough food for the metamorphosis. Another big part of both larvae and pupae were destroyed by parasites as fungi and parasitic wasps as the big and common Pimpla hypochondriaca.

In the spring, April, 1999, the author did not find very many cocoons among the dead leaves on the forest floor, and in September 1999 it was estimated, (Jan Martin), that the density of the attack had decreased with a factor 200 compared to the previous year as is often the case with these mass attacks of C. pudibunda and other Lymantriidae.

Fortunately no harm is done to the trees, as their growth is almost finished when they are being defoliated by the caterpillars, and usuallly the moth population returns to normal size within a season or two.

All photos by P. Stadel Nielsen

From the base of the tree to the top, caterpillars were walking up desperately trying to find food, but only to fall down again and start all over. I was virtually raining with caterpillars!

The colour of the caterpillar of D. pudibunda is normally yellow or bright green, but when ocurring in such huge numbers, they get discoloured in mainly reddish, brownish or greyish tones.

Many trees were surrounded by a 3 cm thick layer of caterpillars on the ground. Lots of caterpillars were dead and the rotten smell of death was already noticeable!

Close-up of the pile of caterpillars. Each larvae is about 4 cm long.