Another new species

On Sunday, Julie Newblé sent us pictures of caterpillars in a tent-web she found strung between blackthorn twigs in the hedge at the top of the Arboretum.

Ian Bushell identified them as the larvae of the small eggar moth (Eriogaster lanestris) and his identification was confirmed by The Wiltshire and Swindon Biological Records Centre. This is a new species for the park and a definite feather in our collective cap: the small eggar moth, formerly a common species, is now listed as Nationally Scarce, due mainly to the gradual destruction of its caterpillars’ hedgerow habitat.

1. Tent-web on blackthorn; 2. Sib-aggregate of caterpillars;

Small eggar caterpillars are social creatures. They exhibit cooperative behaviour in building their shelter, in regulating the temperature inside that shelter, and in defending it against predators and parasitoids; they also seem to leave chemical trails to communicate with each other about nearby food sources. As yet, social behaviour in caterpillars is little understood; most research into social insects has been focused on bees and ants.

The group of caterpillars, called a sib-aggregate or sibling-society, stays together through several instars until they pupate. These pictures are of late-instar caterpillars, close to pupation: they have developed the long irritant hairs that protect them from predators now that they are larger and more obvious mouthfuls.

3. Long irritant hairs on late instar caterpillars 4. Adult moth

Our thanks to Julie for the great photographs. Please do send us pictures that you take of the creatures and plants you find in the park, particularly if you don’t know what they are. The park’s biodiversity is complex and important; the more we know about it, the better we will be able to protect it.


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