This is the bed where my wife and I sleep. I often sit there reading (okay; or playing Draw Something) for a little bit before I turn out the lights.

It was a few nights ago that I first noticed the mysterious ticking noise. Picture me sitting on the right side of the above photo. Linda was on the left side, asleep. As I sat there, I became aware that I was hearing a soft, rhythmic ticking, barely audible, apparently coming from the wall above her head. It was the sort of creaking-house noise one hears from time to time and immediately dismisses.

Except this time I noticed something strange: The noise was repeating. Every 15 seconds or so, a rapid-fire series of clicks could be (barely) heard. Each series of clicks lasted a second or two, starting off fast, then slowing toward the end.

Random household creaks are nothing special. But creaks that exhibit a repeating pattern? What was that?

I leaned over, careful not to wake Linda, and after some cupped-ear investigation I concluded that the sound was coming from the lower right-hand corner of that painting you can see in the photo above. The sound was clearly audible when my ear was within a few inches of that point, but faded when I moved away.

I was intrigued, but I couldn’t figure out what the sound was, so after a few minutes I gave up and went to sleep.

But the next night I heard it again. And when I heard it again on the third night, I mentioned it to Linda.

She was skeptical. This sound was really quiet, and she wasn’t hearing it.

I told her where to put her head, and after a minute she said she thought she heard something, maybe. But she also raised the possibility, half facetiously, that maybe I was imagining it. (TRUE! nervous, very, very dreadfully nervous I had been and am; but why WILL you say that I am mad?)

The next day, when she was out of the house and things were quiet, I went into the bedroom. Sure enough, the corner of the picture was still ticking. After some experimenting with the my phone’s Voice Memos app and Audacity, I was able to get some decent recordings.

Here’s a two-minute stretch of the best one:

The Mysterious Ticking Noise

I came up with two theories for what it might be:

1. It was some kind of sympathetic vibration from a mechanical rumbling too low for me to hear. Some piece of machinery or electric equipment (or something) was sending out a vibration that just happened to be resonating just right with the wood and glass of the picture frame, causing it to make that audible clicking sound.

2. It was an insect of some kind. I’d heard of a “death watch beetle” that supposedly makes a tapping sound in walls; maybe that’s what this was?

Further research has pushed me very much into the latter camp. I think it’s a beetle (or a beetle larva, or some other bug).

Here’s my reasoning: A mechanical source would likely be very regular in the timing of its clicks. A biological source, on the other hand, would show more variation. And these clicks do, indeed, show variation in their timing. Using Audacity I was able to get extremely accurate timing of the clicks, which I put in a Google spreadsheet. It shows the following:

• The number of clicks in each set varies. Most of the sets featured 22 clicks each. About a third of them, though, only had 21 clicks, while one had 23.
• The duration of each set, and the interval between sets, also varied. The shortest set lasted 1.263 seconds, while the longest lasted 1.612 seconds. The shortest set-to-set interval I measured was 9.350 seconds. The longest was 13.811 seconds.
• There were some interesting correlations in the numbers that seemed to support a biological explanation. For example, the longest sets of clicks tended to come after the longest interval from the previous set. That is, a clicking bug that had rested a little longer was primed to produce a more vigorous, longer-lasting set of clicks.

It was neat to be able to examine the clicks with Audacity. By zooming in I could see lots of detail. I’ve included some screenshots below; if you click on them you can see larger versions.

Here’s a view of the whole 2-minute recording. Each set of clicks is represented by a thick line. You can see how the sets of clicks have slightly variable intervals between them:

Here I’ve zoomed in to show three sets of clicks. The individual clicks have started to separate. You can see an interesting shape to each set: The first clicks are quieter (as indicated by the shorter vertical lines representing those clicks). Then they become louder, then quieter, then louder again at the end of the set.

Here I’ve zoomed in to show a single set of clicks. You can clearly see how the clicks slow down over the course of the set, and how they get louder, then quieter, then louder again.

Here I’ve zoomed in to show five successive clicks from within a single set. At this scale something new becomes visible: Each click is actually three clicks. There’s an initial relatively loud click, then a quieter click an instant later, then a barely detectable third click an instant after that.

Here I’ve zoomed in tight on a single click. You can really see that “triple click” nature of the click, and can make fine measurements of the timing (the scale at the top is reading in ten-thousandths of a second). There’s the first (loud) click, then there’s a quieter click 2.4 milliseconds later, and a much quieter click 1.4 milliseconds after that. I wonder what’s causing those. Are they echoes? The sound of secondary impacts, as insect bodyparts strike against each other? Artifacts of my recording process? I have no idea.

I verified that whatever it is is actually inside the picture or its frame; when I moved the painting to the other side of the room, the sound continued to emanate from the painting’s lower righthand corner. We’ve had that picture and frame for just over 25 years, which I know because I bought it for Linda for our third anniversary, and we recently celebrated our 28th. So the wood and paper and fabric in there has had time to get good and old, and presumably tasty to wood-eating insects.

From the Death watch beetle article at Wikipedia:

The death watch beetle, Xestobium rufovillosum, is a woodboring beetle. The adult beetle is 7 millimetres (0.28 in) long, while the xylophagous larvae are up to 11 mm (0.43 in) long.

To attract mates, these woodborers create a tapping or ticking sound that can be heard in the rafters of old buildings on quiet summer nights. They are therefore associated with quiet, sleepless nights and are named for the vigil (watch) kept beside the dying or dead, and by extension the superstitious have seen the death watch as an omen of impending death.

The term “death watch” has been applied to a variety of other ticking insects including Anobium striatum, some of the so-called booklice of the family Psocidae, and the appropriately named Atropos divinatoria and Clothilla pulsatoria.

If you’ve read this far you really owe it to yourself to view the video at Arkive.org of Xestobium rufovillosum making its ticking noise.

Although the sound produced by that beetle is similar to my mysterious ticking noise, the pattern is not a perfect match, making me suspect I’m dealing with a different species. One possible suspect is described this way in my copy of Evans and Hogue’s Field Guide to Beetles of California:

The Deathwatch or Furniture Beetle (Anobium punctatum) (2.7 to 4.5 mm) apparently arrived from Euorpe as a stowaway in imported furniture. It is now established along the Pacific and Atlantic coasts of North America.

I’m going to pester my online friend Charley Eisemen, co-author of what may well be my favorite field guide ever (which is saying a lot, given the way I feel about field guides), Tracks & Signs of Insects and Other Invertebrates. If anyone’s likely to be able to track down the identity of my mysterious noise-maker based only on the sound, it’s Charley Eisemen.

Finally, if you’ve made it this far, and if you’re somehow not among the 125 million who’ve seen it already, I give you the original Mysterious Ticking Noise:

Update: Lang Elliot, co-author of the awesome book Songs of Insects, was kind enough to respond to an email I sent him as follows:

John:

That’s a longhorn beetle larva chewing on wood inside the frame. Before transforming into adults, they are big white grubs with black heads and mouthparts, yummy to eat for woodpeckers at least:

Google Images link

Lang

This entry was posted by jbc on Friday, April 27th, 2012 at 11:54 pm and is filed under animals, net.kooks, science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.