Galls of this species appear at the base of the stem in mid June to mid July ... They mostly occur just above the ground but are occasionally found up to 60 cm above it ... and are surrounded by a rosette of long leaves. It is therefore clear that the gall develops from vegetative buds rather than from rhizomes. The young gall is wide at base and has a tapered tip ... which disappears as the gall matures. During July and August, the gall becomes ovoid, 8–25 mm long and 6–36 mm wide and often changes its color from green to brownish, resembling a small potato.... Galls are spongy and usually multi-chambered, containing 1–30 individual larvae in separate chambers ... As long as the larvae feed, they face downwards inside their chambers, but before the onset of pupation, in early August, they turn to face upwards. Shortly before adult emergence, the gall splits open at its apex into several lobes, similar to the shell of a hickory nut ... Adults emerge from early to late September, after which the gall shrivels and dries on the stem. Emergence of all adults from the same gall may continue over more than a week. Some galls fail to split, resulting in death of the pupae inside the gall. Galls of this species can be very difficult to locate and were rare even in fields where S. juncea was the dominant plant.

Smooth, large, apical gall subtended by leaf whorl...Rhopalomyia hirtipes (Osten Sacken)

Galls are succulent and polythalamous...This species is evidently responsible also for galls on the stolons and crown...