20 Jun 2014

The Singing Lice (that are not lice)

Lepinotus patruelis, a common bark louse. Photo by David Jones
By Judy Wearing

“I think I have insects in my house,” the Bavarian woman living in England told the secretary at the Department of Zoology where I worked. “I hear these knocking sounds all the time. I think it is an insect. Do you have anyone who could come and check it out for me and tell me what it is?”
The deathwatch beetle, which hits its head against wood to call for a mate.
Photo by Josef Dvořák.
One candidate for the cause of the sounds she was hearing was the deathwatch beetle, a small insect with a hard head that burrows into wood beams. The beetle knocks on wood to attract mates, making a noise that sounds a little bit like a miniature woodpecker. People don’t want deathwatch beetles in their houses, because when the larvae burrow/eat their way into wood beams they leave tunnels behind. The tunnels weaken the beam and can cause structural damage.

I went to this woman’s house looking for another kind of insect, however. I was looking for Psocoptera, a group of tiny insects otherwise known as bark and book lice, or barkflies. Measuring from 1 to 2 millimetres in length, these obscure creatures are not lice at all, but rather distant cousins. They have long antennae, and many species lack wings. They feed on tiny bits of this and that: algae, crumbs of other insect carcasses, and fungal spores. They do not bite anything, and frankly, they can seem rather boring. You might find them on logs and tree trunks, the undersides of mushrooms, or other damp places – if you look closely enough. But, they are easy to ignore, and largely go unnoticed.
Trogium pulsatorium, whose mating call sounds like the ticking of a clock.
Some book and bark lice have a remarkable habit: they ‘sing’. One species, Trogium pulsatorium, creamy white from head to toe and small enough to fit on the end of a pin, produces a noise that sounds exactly like the ticking of a clock. I'm inclined to think this creature is the original deathwatch, rather than the woodpecker-like beetle. The death watch was a sound in people's houses that terrorized Medieval Britain. The ghostly ticking of a clock was thought to mark the final hours of someone in the household. The female bark louse makes this ticking noise by vibrating its abdomen. Like the noise of the deathwatch beetle, it is a mating call.

Lepinotus patruelis female, who 'sings' to attract mates by vibrating her abdomen.
Photo by David Jones
Another singing barklouse, Lepinotus patruelis, is slightly more colourful. Females are dark brown, and nearly 2 mm in length, so their rear ends might dangle off the head of a pin. The males are smaller and golden brown. In this species, when males vibrate their abdomens, they make a sound like a quacking duck. Quack, quack, quack – four to six times. They do this several times a minute when calling for a mate. When females vibrate their abdomens, they make a series of clicks like dragging a fingernail across the teeth of a comb. The ‘songs’ are used by both males and females to attract mates. Both sexes, especially females, keep singing when a mate draws near. And females seem to compete with each other, just like male crickets do, by singing at each other in the presence of a male. To hear these noises in the laboratory, I used a listening device, a sound magnifier, sold at a local electronics shop. The insects are pretty tiny, so it is not surprising that their sounds are not audible to the naked ear. If, or how, the Bavarian woman could hear these insects added to the mystery.

I searched out places in her main rooms where these bark lice might hide. In the kitchen, around the counter there were lots of bread crumbs and some mold spores in the corners of the window sill. In the living room, there were plenty of tropical house plants, and the air was warm and moist. Perfect conditions for these insects: damp with lots of food. As I sat on the sofa with a cup of tea in hand, I heard the sound of a fingernail running across a comb. I listened and heard it again. It was a female Lepinotus patruelis, calling to attract a mate.

And I could hear it loud and clear! I followed the persistent noises to a large tropical plant in the corner, and began searching among the leaves. I found her nestled in the crux of a large, curved leaf – she had found a natural amplifier and was using it to broadcast her song to the whole room.

This feat, of finding an amplifier to broadcast their sound makes these bark lice the smallest known creature to make an audible noise (to my knowledge). But this broadcasting skill is not the only unusual feature of the singing behaviour. It is also highly unusual for females of any species to be the ones calling for mates, let alone competing in 'singing competitions.' But that is another story, for another blog.

Wearing, J. (1996) Reproductive biology of Lepinotus patruelis (Psocoptera): Implications for courtship theory. (Unpublished doctoral dissertation) University of Oxford, UK.

Death Watch Beetle (Xestobium rufovillosum)



Unknown said...

Hello :) i hear the same noises every day! I live in a small flat in germany, stuttgart and thought it was something behind the wall. On some day i hear the "quack" noise near my bed and found a very small dark brown insect. And this insects make the noise. I can hear it because they use different locations for example plastic bags or cartons and then i can hear them. It seems they love old paper, cartons etc.
Sometimes i can hear the click noise too....
But this duck noises are the worst. I ask people in german insect forums but nobody answered so it seems that they think this noises doesnt exist. You should write it down on wikipedia so maybe other people hear this noises too but nobody can help them

Unknown said...

I hear the females quite often but not the quack noise yet! We get them in our tortoise vivariums and in cupboards and anywhere there are natural fibres like hay or straw. Amazes me how something so tiny can be so loud! Now I know they broadcast their sounds I'll know to look for natural amplifiers ��

Sig. Galvani said...

Thank you for this post!

I find these creamy ones (trogium pulsatorium) here and there quite often in my house but i only notice them tapping when I'm working in my office (where i also keep my books) at night, in silence. And it's so annoying! I've read about them before but they are so small and fragile that i was finding it hard to believe they could make such an audible sound!

Is it possible to know an approximation of the bpm (beats per minute) of the tapping noises? If what i'm thinking is right, the creamy ones have tappings of about 300 to 320 bpm. Can anyone confirm? (you can use this bpm calculator: http://www.beatsperminuteonline.com/ )

As for other noises, is this the nailed comb teeth (you might have to turn the volume up)?

And I don't think I ever heard the quack sound - Guess that's a good thing ^^'

Also, if you're interested: where I first read about this noisy little bugs (the fisrt one is really funny, and that's where i've found the nailed comb sound):



CraigP said...

I spent 25 years trying to explain to people exactly the noise that you ascribed to the Lepinotus patruelis and have never been able to record or explain the tiny quack quack quack noise which I thought was coming from my walls. I've recently heard the noise in another house and thought I would have another look online, and I'm very glad I found this page as it's answered a lifelong mystery. Cheers!

Anonymous said...

I had one about 2 years ago in my kitchen. That's when I found this page, which confirmed, that I wasn't imagining things. The next day some ants carried a dead one from under the cupboards, where I couldn't reach without dismantling the kitchen. That's when the noise stopped.
Now they are back again �� I hate this noise. They always use the cupboards as amplifier. Hope I can get rid of them, before there is an invasion.

Anonymous said...

I had this quack-noise which I would describe more as like scratching with fingernail over a toothbrush - mostly for five times in a row - about 2016 for several month.
After I found and killed one tiny light brown insect which was crawling in my wardrobe is was gone till it returned some weeks ago.
I vacuum-cleaned like mad, I sprayed cans of insect spray but nothing helps:
Every night the 'schrap-schrap-schrap-schrap-schrap' sound starts again. It is so annoying! The only thing that helps a little bit is extreme airing - the 'schrap-schrap-bug' how I call them now seems to need high air humidity.