The beetle is elongate, ranging from 1½–2½ mm in length, and a dark brown, with yellow legs and antennae. The head is larger than the thorax, with large eyes protruding from either side.
The larvae are wood-borers that feed on moist and decaying chestnut and oak logs. They have also been reported as causing damage to buildings and poles (hence the name); however, reports of the species are infrequent and it is unknown whether they are rare, or common and unrecognized. The life cycle is unusual in that the cerambycoid stage of the larva can either develop into an adult female, or give birth to caraboid larvae. The species has been spread to various parts of the world by human commerce, probably in timber.
Classification of Micromalthus debilis is controversial and unsettled. The species, first reported by LeConte in 1878, was long considered one of the Polyphaga, and placed in Lymexylidae or Telegeusidae, or as a family within Cantharoidea. However, characteristics of larvae, wings, and male genitalia show that it must be in the suborder Archostemata.