Last modified: Aug. 7, 2019, 7:02 p.m.
In Belgium, this is not a rare but rather a local species that can occur even very numerous at certain locations.
The tri-valved case of this species is small measuring 4–5 mm and is often covered with small black droppings from the caterpillar. Occasionally there are also faint light longitudinal streaks. The mouth angle is 10°–44°.
See also bladmineerders.be.
The eggs are deposited on the flowers of the hostplant. Juvenile larvae live, without forming a case, inside a seed granule, feeding on it. Only when the larvae almost reach maturity that a small case is constructed. The latter is difficult to find between the seed-heads but the best period is September. The caterpillars are full-grown in October, mostly leave the hostplant and hibernate at ground level. only occasionally they stay hidden between the seeds. Next spring, the pupation takes place inside the case.
C. caespititiella is significantly less often observed than other Juncus-feeders because of the more hidden lifestyle.
The adults fly in May and June. Rarely, some specimens have been observed well into October.