Large size, general orange-brown colouration with darker markings on anterior of pronotum in males; ventral side mostly bronze-grey with hairs relatively inconspicuous.

This is the largest Buprestid in SA and can be over 60 mm long. In exceptional years it appears in huge numbers, together with T. stevensii (on Eyre Peninsula) and, to a lesser degree, T. parvicollis. In intervening years it is only present in low numbers or hardly at all. The major episodic outbreaks are erratic and difficult to predict, but may be related to life-cycle cohorts and be triggered by major rainfall events. At such times the mallee country comes alive with helicopter-like buzzing as these large beetles lumber from canopy to canopy to feed on Eucalypt blossoms. Their emergence in mid to late summer coincides with the peak-flowering of Narrow-leaf Mallee Eucalyptus leptophylla, which is the principal adult host.

Although recorded on a variety of Eucalyptus species, as well as Dryland Tea-tree Melaleuca lanceolata, Narrow-leaf Mallee E. leptophylla greatly predominates as an adult host. The presentation and arrangement of its nectar-rich blossoms is well-suited to this and other large Buprestids. Flowering occurs en masse and renders whole sections of the outer canopy creamy-white, allowing the beetles to move about freely.

French 1911 reported adults feeding on flowers of Melaleuca uncinata (Broombush). The reference to adults feeding on flowers of Melaleuca pauperiflora (Boree) by Hawkeswood 1980b and cited in Bellamy et al. 2013 is in error for M. lanceolata (Dryland Tea-tree). The former flowers in spring, the latter in summer which is when T. heros emerges. Hawkeswood expressed uncertainty as to which of these was the correct ID and opted for M. pauperiflora. However voucher specimens (to which he refers) collected on that date and held in the PERTH and Adelaide (AD) herbaria as T.J. Hawkeswood 185 are now determined as M. lanceolata.

Tepper 1887 provided an early breeding record for it (as Stigmodera heros) in Eucalyptus lignotubers, or 'mallee stumps': 'The larvae of this, and the next four species inhabit the so-called mallee roots, the subterranean trunk of Eucalyptus uncinata [misapplied for E. leptophylla in SA at that time], E. oleosa, and E. gracilis. They attain a length of three inches [75 mm]; require at least two years (probably four) till maturity, and are sometimes found numerously therein. .. I found once many hundreds in a small load.' Tepper's statement of five Temognatha species breeding in three Eucalyptus species is taken as a general supposition, and is not interpreted to mean that he had found breeding evidence for all five of his species in each of the Eucalypts.

A Temognatha larva I extracted from a root at the base of a Gilja mallee Eucalyptus brachycalyx on Eyre Peninsula in November 2022, was identified as T. heros in May 2024 by its DNA barcode (mitochondrial CO1 sequence).