Last modified: May 18, 2019, 6:12 p.m.
This is a local species in Belgium, mainly in the Kempen and in the southern part of the country.
S. spheciformis is one of the larger clearwing species in Belgium (23–32 mm). It is easily recognisable by the almost completely black colouration and only one yellow band on the abdomen. Also a striking feature is the pale yellow colouration of the distal part of the black antennae.
This species is reasonably well attracted by the pheromone originally developed for S. tipuliformis.
The caterpillars construct galleries between wood and bark if they live in larger trees (often the remaining stump of a cut tree). If they live in smaller stems (the most common situation) a gallery, going downwards into the root-system, is constructed in the centre of the stem.
This species does not construct a cocoon and, hence, the pupa can freely move up- and downwards in the gallery.
The female lays the eggs at leaf undersides of the foodplants. The young larva migrates towards the base of the stem and lives there from the sap flow between wood and bark. After the first wintering, the larvae start to make mines in the wood too and also construct a gallery in the central part of a stem.
Before the second hibernation the caterpillar enlarges that shaft and, at the end of it, bends it outwards towards the bark to construct the future exit hole only leaving a thin layer of the bark.
In Alnus, having a smooth and thin bark, this "membrane" discolours reddish to brown or even a almost black. When living in Betula, having a more rough bark, the future exit hole is invisible from the outside. Next springtime, the larva pupates without constructing a cocoon. The pupa is very mobile in its gallery, providing the possibility to respond to weather conditions or external disturbances. When hatching, which mostly takes place in the late morning hours, the pupa breaks through the bark membrane and slides out halfway. The exit hole is always quite low in the stem and is rarely found higher than 25 cm above ground level.
The adults fly from mid May till the end of June.
The preferred habitat are moist and even marshy places where the main hostplant Alnus is common. In dryer areas also (young) Betula trees are taken beside Alnus. This is often the case in heath landscapes that have generally a lot of young Betula trees but also young Alnus trees in the vicinity of fens.
In domesticated areas this species can be really abundant in the new shoots formed by regularly cut Alnus trees at the borders of fish ponds.