Deathwatch beetle

The deathwatch beetle (Xestobium rufovillosum) is a species of woodboring beetle that sometimes infests the structural timbers of old buildings. The adult beetle is brown and measures on average 7 mm (0.3 in) long. Eggs are laid in dark crevices in old wood inside buildings, trees, and inside tunnels left behind by previous larvae.[1] The larvae bore into the timber, feeding for up to ten years before pupating, and later emerging from the wood as adult beetles. Timber that has been damp and is affected by fungal decay is soft enough for the larvae to chew through. They obtain sufficient nourishment by using a number of enzymes present in their gut to digest the cellulose and hemicellulose in the wood.

The larvae of deathwatch beetles weaken the structural timbers of a building by tunneling through them. Treatment with insecticides to kill the larvae is largely ineffective and killing the adult beetles when they emerge in spring and early summer may be a better option. However, infestation by these beetles is often limited to historic buildings, because modern buildings tend to use softwoods for joists and rafters instead of aged oak timbers, which the beetles prefer.

To attract mates, the adult insects create a tapping or ticking sound that can sometimes be heard in the rafters of old buildings on summer nights; therefore, the deathwatch beetle is associated with quiet, sleepless nights and is named for the vigil (watch) being kept beside the dying or dead. By extension, a superstition has grown up that these sounds are an omen of impending death.

The deathwatch beetle is part of the beetle family Ptinidae, formerly known as Anobiidae. This includes a number of subfamilies including Ptininae, the spider beetles which are mostly scavengers, Anobiinae, wood-boring beetles, and Ernobiinae, deathwatch beetles, also wood-borers. In 1912, Pic erected Ernobiinae for beetles previously classified under Dryophilini by Fall in 1905. White elevated this taxon to subfamily status in 1962 and 1971, and in 1974 included 14 genera in the subfamily.[2]

The eggs are white, slightly pointed at one end and sticky.[3][4] Eggs measure on average 0.7 mm (~0.03 in ) in length and 0.5 mm (~0.02 in) in width.[1]

The larvae are creamy-white with six legs, black jaws, a pair of eyespots on either side of the head. They grow to about 11 mm (0.4 in) long making them the largest Ptininae found in Britain. These larva are distinctive due to a swollen thoracic region and multiple golden setae.[1]

The pupa, when newly formed, is shiny and milky white in colour. They will gradually darken as they mature and produce eyes, tarsi, and “teeth”. During this stage of development, they will completely change appearance by forming a head, complete eyes, mouthparts, antennae, and legs. The pupa measures 7–8 mm in length and around 3 mm in width.[1]

The adult deathwatch beetle is cylindrical measuring on average 6 to 7.5 mm (0.24 to 0.30 in) long. The head is largely concealed by a brown thoracic shield. The shield and elytra are dark brown or reddish-brown, with a patchy felting of yellowish-grey short hairs. The antennae have eleven segments, the distal three segments are somewhat enlarged.[3][4]