Last modified: June 17, 2020, 12:42 p.m.
This is a rare and local species in Belgium, known only from the southern and eastern part of the country.
S. scoliaeformis is a large species (25–35 mm) that can be recognised by the extensive transparent areas and the colouration of the anal tuft (orange-brown in males and brighter orange in females). The antennae are black but with pale yellow scales distally. This is especially striking with the females where almost half of the antennae is almost white. Dorsally, the abdomen has 2 yellow bands. The proboscis is, as in all species of this genus, well developed and functional.
The adults are attracted quite well by a pheromone developed for this species.
The egg is brown and has a white net-shaped structure on its surface.
The caterpillar is off-white and has a brown neck-shield, typical for Sesiidae.
The exit holes, having a diameter of 4–5 mm, can be found on the trunk of old Betula (birch) trees from ground level to about 2 m high.
The female deposits the eggs on the bark of Betula trees, often near old exit holes or on cancerous swellings. But these trees must be old enough before they will be used by females for ovipositing. Typically, the trunk is not smooth and white anymore but dark brown-black, rough and deeply carved. In many cases the same tree is used for many years resulting in a so-called "breeding tree".
The young larva lives between bark and wood and feeds on the cambium sap of the tree. The caterpillar winters in a silken cocoon: a hibernaculum. In the second year, the larva enlarges the gallery. Often there is only one rather short gallery that is made mostly in the inside of the bark and not into the wood and is typically flat and broad. After the second hibernation, that again takes place in a white silken cocoon, the larva enlarges the gallery a little bit to typically about 7 cm. Non used parts of it are often filled with moist dark brown frass and the larva lives in a black coloured and very wet environment caused by the copious amount of sap. Generally in May, the caterpillar constructs a gallery towards the outer surface of the bark leaving only a thin layer of bark, separating it from the outside world. Directly underneath the future exit hole, a strong and firm cocoon is constructed from dark brown wood-grains from the bark. This cocoon is lined at the inside with spun silk. On hatching, the pupa works his way out through the covering lid or pushing it aside and hatches subsequently. As usual, the exuvium stays partly in the bark for some time.
The adults fly from late May till mid July.