Last modified: April 12, 2020, 7:07 a.m.
S. formicaeformis is a very common species throughout Belgium.
S. formicaeformis is a rather small species (14–24 mm). The bright red wingtips, the large transparent areas on the forewings and the single red band on the abdomen make this species very distinguishable. The proboscis is, as in all species of this genus, well developed and functional.
The males are very well attracted to the pheromone developed for this species and are best lured in early afternoon although the optimal time span is very weather dependent.
In most cases only short galleries are constructed.
The eggs are sometimes deposited on a twig of the hostplant but in most cases they are laid near damaged parts of the trunk or twigs. The females appear to prefer cancerous swellings, both on trunks and twigs for ovipositing. These often very irregularly formed swellings are in most cases caused by Agrobacterium tumefasciens, a soil bacterium. Here, the larvae live in rather short galleries between dead and living parts of this so called 'crown gall'. Occasionally, when there is no living tissue available anymore in smaller galls on branches or twigs , the larvae leave the gall and make longer galleries in the twig. Often the galls show pecking traces caused by birds, in many cases various tit species or sometimes woodpeckers.
After the hibernation, that takes place inside the gallery, the caterpillars construct an exit gallery to the surface of the bark, leaving a thin layer of wood as a separation with the outside world. Parasitism by flies (mostly Tachinidae) or wasps (mostly Ichneumonidae) can be considerable.
Pupation takes place in a cocoon made from gnawed plant particles spun together. On hatching, the pupa works its way out through the cocoon and remaining thin bark layer. At the relative low altitudes in Belgium the development always completes in one year.
The adults fly from May till the end of August. Occasionally, a few specimens can still be observed in the beginning of September.
The larva develops inside the trunks, stems, branches and twigs of various Salix species.
S. formicaeformis occurs in virtual all places where the hostplant Salix spp. occurs. Therefore swamps, and in general biotopes in the neighbourhood of water, are the preferred habitat of this species.