New Forest Bee-Fly

Thyridanthrax fenestratus

The Mottled Bee-Fly (Thyridanthrax fenestratus) is not something you see everyday. Or ever before as far as we were concerned.

So it was a nice surprise to find this individual sunning itself on a gravel path at Pigbush in the New Forest. The Mottled Bee-Fly requires sandy or gravelly locations as it relies on the host wasp which creates its burrows in these areas. Damage to the burrows of the host wasp and loss of suitable habitats for the wasp has meant the Bee-Fly has previously been under threat.

The Mottled Bee-Fly is a parasitoid of the sand wasp (Ammophila pubescens) or of the caterpillars gathered by the wasp for its larvae. This means that the bee-fly larvae develop inside either the larvae of the sand wasp or inside the caterpillars that the wasp collects; the host dies as a result of the development of the bee-fly.

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This is a ‘thermophilous’ (heat-loving) species, and occurs only in warm areas so this warm path in the summer sun was ideal. The adults feed on nectar, so a source of flowers is essential and the combination of heather and gravel or sand is the perfect combination.

Any records should be submitted to http://www.brc.ac.uk/irecord/