Last modified: Aug. 7, 2020, 10:35 a.m.
This is a local species mainly observed in the northern part of Belgium.
S. bembeciformis is one of the largest clearwing species in Belgium (30–50 mm) making it, on average, only slightly smaller than S. apiformis, its closest congener. Females are, in general, considerably larger than males. It resembles a big hornet (Vespa crabro) really well.
Two features allow to distinguish this species easily from S. apiformis: it has a yellow neck-collar and misses both yellow 'epaulettes'. The proboscis is strongly reduced and non-functional.
There is, at present, no artificial pheromone available for this day-active moth,although they are very easy to attract to the pheromone of Opogona sacchari.
The eggs are coloured red-brown.
The eggs are laid on the bark of the lower part of the tree, most likely close to an injury or another suitable entrance possibility into the tree. The caterpillar develops during 3 – 4 years in the trunk.
The first year larva lives superficially under the bark feeding on the sap of the tree. Very small amounts of frass are protruded. After the first wintering, the larva goes deeper into the trunk and, mostly, also into the root making several galleries. At this time, the cross-section of these galleries is somewhat ellipsoid. After the second hibernation the caterpillar constructs galleries with a circular cross-section and builds, in the autumn, the pupal chamber in a loose cocoon and also the future exit hole which is always located lower than the pupal chamber. This makes it necessary the larva will pupate orientated head down to be able to hatch. This is an important difference with S. apiformis, its closest relative, where the cocoon is located below the future exit hole and, as a consequence, pupates head up.
The pupation takes place in the following spring and so the caterpillar is in the pupation chamber all winter long. Often, once in their pupation chamber, the caterpillars and pupae are heavily predated on by woodpeckers. This is clearly visible by the chisel traces caused by this bird to reach it's prey. Prior to hatching, the future exit hole is often open already because the thin layer of bark covering the exit hole shrinks during winter and tears off. Only rarely the lid is still present.
The adults fly from early June till mid August.
The larva lives for 3 – 4 years in the stem and root of a wide range of Salix (willow) species but apparently prefers broad leaved species.