Excavator: Stems. Female Hoplitis claviventris commonly excavate their linear nesting burrows in dead, dry, pithy stems, including Senecio (Hallett, 1928), Rubus and Rosa (and Sambucus, Verbascum, Artemisia, Onopordum, Cirsium, Arctium). Several nests have been found in Rubus stems lying on short downland sward in open sunlit situations in Kent and Hampshire (pers. obs.). The species has also nested in a buried Rubusstem (R.C.L. Perkins, 1886). Females have also been observed burrowing into an old paling (Arnold, 1903), and into decaying roots beneath the soil (R.C.L. Perkins, 1923). It has also nested in the soil (E. Saunders, 1896a), and in a vacated gall of the chloropid fly Lipara lucens on a Phragmites stem (Blüthgen, 1919).
The cell partitions and closing plug comprise masticated plant pulp, which is green when fresh, but later becomes a dark brownish colour. It is possible that other ingredients are incorporated in the pulp as, when magnified, these partitions frequently appear waxy with granular and grit-like inclusions. The inner surface of the burrow serves as the lateral cell wall, no leaf mastic being added to it. Nests generally contain only a few cells (the average being about four), but a few contain far more: Höppner (1904b), for example, found 12 in one nest. The cells are barrel-shaped and are about 7-13 mm long and 3-4 mm wide (Danks, 1971b). Those nearest the nest entrance invariably produce males, whereas those towards the rear of the burrow produce females; the species is markedly protandrous. Nests in Rubus stems have been described by F. Smith (1844d, 1845a), Höppner (1904b), Enslin (1925) and Micheli (1930); additional nests are figured by F. Smith (1844d, 1845a) and Höppner (1904b).
The mature larva or prepupa has been described and illustrated by Enslin (1925) and Micheli (1930). When fully developed, the prepupa spins a thin, papery, brownish cocoon. This is semi-transparent, enabling the pale yellow prepupa, with its head and thoracic segments, and posterior abdominal segments characteristically curved inwards, to be easily viewed within. It is in this stage that the species overwinters.
Westrich (1990) states that females nest in the pith of dry stems of Arctium spp., Cirsium spp., Onopordum spp., Rubus spp., Sambucus spp. and Verbascum spp.