[4] Trapezites iacchoides adults are brown above and pinkish-grey below with yellow or orange markings on the wings and a wingspan of approximately 36 mm (1.4 in).

Eggs are dome shaped, cream in colour, measuring approximately 1.4 mm (0.055 in) in diameter with 19-21 longitudinal ribs.

Pupae are pale brown, covered with a waxy white powder, measuring up to 23 mm (0.91 in) with a short bi-lobed lateral projection on the head.

Adult females tend to remain close to their breeding areas, laying their eggs singly on the leaves of the species' host plant, the spiny-headed mat rush (Lomandra longifolia).

Pupation occurs inside the larval shelter, head pointing upwards.