Tick, tick. Tap, tap, tap. These sounds are produced by a deathwatch beetle (Xestobium rufovillosum). Old buildings can sometimes give us spooky vibes. However, for the deathwatch beetle, they are quite welcoming. This is because these beetles are woodboring and oftentimes infest lumber of old buildings. Woodboring beetles comprise of many different species of beetles that eat wood. This can be the larval or adult stage (beetles go through complete metamorphosis like butterflies do). The natural history of woodboring beetles varies depending on the species in question, however, many species of these beetles tend to select dying or dead trees. For the deathwatch beetle, very old wood is preferred and only the larvae feed. The adults do not feed and are short lived.
So that explains why the deathwatch beetles are in buildings, but what about the “creepy” tapping? Simply put, it is communication via sound. Deathwatch beetles produce the sounds by tapping their heads on the substrate (timber), which helps males find the females. Both sexes tap, but it is a mechanism in which females are advertising. Females will only respond to male tapping if they are interested in mating. Females do not respond to female taps. There are 4-11 (I’ve seen this number range vary in the literature) strikes in a “tapping bout.” Males will suddenly decide to start tapping in hopes that a female is listening. If a female wants to mate, she will respond to the potential mate’s taps by tapping a reply. This helps him locate her.
The biology of deathwatch beetles has resulted in superstitions and folk beliefs. Due to tapping inside buildings and people hearing the beetles’ sounds when quiet, superstitions of a warning of death have propagated throughout history. Think of it. You’re in an old house and in the middle of the night, suddenly you hear tapping. In a very quiet room, tap, tap… An ominous feeling may overcome you. In European folklore, deathwatch beetles are connected to the death of a member of the household in which the tapping occurred. This is because in ancient Britain people typically died at home. The death vigil (or death watch — hence their name) was thought to cause the tapping to be heard when the house was quiet, as people typically are when someone is on their deathbed. This led the deathwatch beetle’s tapping to later be correlated with the Grim Reaper because the tapping noises were heard in silent homes and people began to think the sound was a bad omen meaning death.
Fear not. Although the sounds have been correlated with death, correlation doesn’t necessarily mean causation. Enjoy the spookiness if you like the folklore, but also realize that deathwatch beetles are making tapping noises to attract a mate, not predict death. Unraveling mysteries like these can help us better understand our world and help us have less fear.
For my blog article today, we posted a poll on Twitter and the blog asking for input last week. There were three ideas and they all had a “spooky” theme. You know, because it’s October and all. Unfortunately, I forgot to post the Twitter poll on the last post on this site. Therefore, we are going to write about both deathwatch beetles and forensic entomology. This is because the deathwatch topic received the most votes on Twitter, but forensic entomology was the only comment on the blog post asking for input on what to write about. So keep an eye out for a forensic entomology article soon!
It was fun reading and writing about Deathwatch beetles. They are a neat example of sound communication in insects and long-standing folklore.
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Birch, M. C., & Keenlyside, J. J. (1991). Tapping behavior is a rhythmic communication in the death-watch beetle, Xestobium rufovillosum (Coleoptera: Anobiidae). Journal of insect behavior, 4(2), 257-263.
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