Termite
Head-Banging: Sounding the Alarm
|
|
Tom Fink (tfink@olemiss.edu),
Lichuan Gui, Yong Wang, Zhonghua Cao, Adarsh Jaiswal, Orwa Tahaineh, Vijay
Ramalingam, Roger Hasse, *Alan Lax, John Seiner
National Center for Physical Acoustics
1 Coliseum Drive
University of Mississippi
University, MS 38677
*USDA ARS, SRRC
1100 Robert E Lee Blvd.
New Orleans, LA 70124
Popular version of poster paper 5aAB7
Presented Saturday, December 2, 2006, at 8:00 AM
152nd ASA Meeting, Honolulu, Hawaii
|
|
Introduction |
|
Figure 1. Formosan Subterranean
termites: Soldiers have the dark amber colored heads and dark pointy
mandibles. The rest of the termites seen here are workers. |
Subterranean
termites are very weak and fragile insects. When placed in a
small open petri plate termites can not escape and will rapidly
dry out and die. Ants and other predators can easily overpower
exposed termites. To avoid these perils subterranean termites
tunnel in the ground and wood and wall everything out. Thus to a
subterranean termite any breach of their tunnels or carton nest (a
structure made of undigested cellulose, mud and termite saliva and
punctuated by a maze of tunnel-like galleries) is a cause for
alarm. When the Formosan subterranean termite (FST) (Coptotermes formosanus) and the native
subterranean termite (RF) (Reticulitermes flavipes) detect a
potential breach, the soldiers will usually bang their heads apparently to
attract other soldiers for defense and to recruit additional workers to
repair any breach. In the video below (Video 1)
taken inside a Camphor tree infested with a large population of FST you will
see a soldier on the right banging its head very hard on the carton nest
substrate while an adjacent soldier on the left tremulates (rapidly moves
forward and backward without moving its legs). |
|
|
Video 1: Click the picture above to see video
of FST head-banging and tremulation in a Camphor tree. |
|
Head-banging results in the strongest substrate
vibrations/loudest sound that termites make. The sound of a large number of
FST soldiers head-banging in a large River Birch tree in New Orleans can be
heard in Sound Clip 1. This is a much
more amplified vibration/sound than caused by chewing (see
Sound Clip 2 below, from the same tree
and recorded in the same way with the same settings). Chewing in most trees
and structures is usually much more reduced in amplitude than recorded in
Sound Clip 2.
Sound Clip 1: Click the
speaker icon to hear termite head-banging from a River Birch tree. |
|
Sound Clip 2: Click the
speaker icon to hear termite chewing from the same River Birch
tree. |
|
|
Head-Banging Details |
In the second
video below (Video 2) you will see a
view inside an FST infested Black Willow tree. The central channel is the
drill hole that allowed entry of the borescope video camera, while to the
sides is the carton nest. A soldier can be seen vigorously head-banging for
2.5 minutes. Near the end of the clip another soldier joins, even more
vigorously. Notice also that most of the soldiers are NOT head-banging.
Perhaps some soldiers are more inclined to head-banging than others. |
|
Video 2 (without sound):
Click the picture above to see video
of FST head-banging in a Black Willow tree. |
In Video 3 below
you are looking into a natural carton nest in a Slash Pine tree heavily
infested with FST. No soldiers are seen head-banging in this video clip but
three workers are (indicated by a red and yellow star). While the soldiers
(Videos 1 and 2 above) flatten their heads and hit the underside of their
heads, workers hit the substrate with their mandibles as they do not flatten
their heads at all. Workers also only head-bang briefly. The head-banging
sound you hear in Video 3 is from soldiers elsewhere in the carton nest. |
|
Video 3: Click the picture above to see video of FST
workers head-banging in a Slash Pine tree. |
In Video 4
two RF soldiers are observed to be head-banging vigorously.
Despite having larger heads than FST, RF head-bangs faster. RF
soldiers will readily head-bang outside their nests and galleries when
provoked, while FST rarely do so. |
|
Video 4 (without sound): Click the picture above to
see video of two RF soldiers head-banging. |
In Video 5 below
you will hear a single RF soldier head banging for a long time. The average
time between successive head-bangs in this soldier is 0.044 seconds (average
of 31 inter head-bang periods). RF soldiers typically head bang in bursts
of 3-4 head bangs. This pattern of 3-4 bangs in a burst is often easy to
recognize with the ear. FST usually do not head-bang in bursts but rather
have a steady uniform head-banging pattern. |
|
Video 5: Click the picture above to see video of the waveform of one RF soldier head-banging. |
In the Video 6
below you will hear a single FST soldier head-banging (the clip will repeat
four times). The average time between head-bangs in this clip is 0.066
seconds. Often the time between head-bangs in FST is longer. |
|
Video 6: Click the
picture above to see video of the waveform of one FST soldier head-banging. |
|
Further Details of Head-Banging As Observed with High-Speed
Video |
Because FST
and RF head-bang so fast the details can not be seen with the eye. Using
high-speed video we can see the details as shown in this video of RF shown
in slow motion (Video 7, original
video taken at 10,000 frames per second, and shown here at 30 frames per
second). In both species, RF and FST, the head is raised up by moving the
prothorax up at its articulation with the mesothorax (the head is attached
anteriorly to the prothorax, which possesses the first pair of legs, the
mesothorax contains the second pair of legs and is attached to the prothorax
by a movable junction). The legs are not used to raise the head. The head
is then rapidly moved down like a battering ram and the head hits flat on
the substrate. What can only be seen in slowed down views of high-speed
video is that the head often rebounds, or bounces up after the initial
impact and then hits the substrate again in about 4 milliseconds. This can
be seen on head-bangs 1 and 3 in video 5. This rebound substrate hit
produces an additional substrate vibration. |
|
Video 7: Click the
picture above to see video of
one RF soldier head-banging. |
While similar
in body size (but larger in head size), the native termite generally raises
its head higher (up to 2 mm) than the Formosan termite (about 1mm).
In order for Reticulitermes to head-bang faster (shorter duration
between successive head-bangs) it must accelerate its head faster and show a
higher velocity than for FST specimens. Upward and downward head velocities
in the FST specimen are respectively 100 and 240 mm/sec, while
the values for Reticulitermes are over 200 and about 400
mm/sec. Similarly acceleration values for FST soldiers are about 400
m/sec2 vs up to 700 m/sec2 for
Reticulitermes. |
|
Practical Use of Head-Banging by Humans |
Because termite head-banging results in the loudest and most diagnostic
sound that termites make, it can be utilized for termite detection.
The most difficult part of termite control is termite detection due to their
subterranean and hidden tunneling habits. A useful sensor for termite
vibration (due to head-banging and chewing) is a 1000 mv/g
accelerometer (Figure 2). Termite
vibrations are transmitted to the accelerometer sensor by a waveguide (bolt,
screw, metal rod, etc.) which causes the piezoelectric material of the
accelerometer to produce an electrical signal in proportion to the amplitude
of the vibration. These electrical signals are then amplified by a signal
conditioner and transduced into sound that can be heard through headphones
or recorded. |
|
Figure 2: Accelerometer,
waveguide, signal conditioner and headphones used to detect head-banging of FST
infesting the floor below the linoleum tiles. |
Detection of subterranean termites by head-banging,
especially FST (due to their higher percentage of soldiers per colony,
approximately 10%, than RF at approximately 1%) is especially useful for
trees. FST infested trees possess a carton nest at the base of the
tree. Placing a waveguide in a tree crotch gets close to the carton
nest/galleries and induces head-banging. A total of 1957 trees were
examined in New Orleans City Park visually (termite mud tubes, wood damage,
termite mud packs at tree base, observing termites while removing soil at
the base of the tree) and acoustically (using a 1000 mv/g accelerometer and a 35 cm long
metal wave guide inserted into all tree crotches if necessary). Five
hundred twenty-eight trees or 27% were infested with FST. Fifty one percent
were missed by visual methods alone while only 3% of trees were missed
acoustically (but termites were found visually). Head-banging is so
distinctive and often loud that "listening" to termites in noisy urban
environments is not usually a problem. In Jackson Square, New Orleans
head-banging in two Aristocratic Pear trees could easily be heard above
intense urban noise including the sounds of street performers and their
cheering crowds (see Figure 3 below
and associated Sound Clip3). |
|
Figure 3: Two heavily FST
infested Aristocratic Pear trees (tree 86 is distal to 85 alongside the
bench) in Jackson Square Park in New Orleans, November 2003. Both of these
trees appeared not to be infested by visual methods but loud head-banging
was detected acoustically.
Click the picture above to hear termite head-banging (Sound clip 3) in tree 85 along with
background sound from the crowd cheering for the street performers |
|
Selected Representative Literature |
Connetable, S., A. Robert, F. Bouffault and C. Bordereau.
1999. Vibratory alarm
signals in two sympatric higher termite species: Pseudacanthotermes spiniger
and P.
Militaris (Termitidae, Macrotermitinae). Journal of Insect Behavior 12:
329-342.
Kirchner, W.H., I. Broecker and J. Tautz. 1994. Vibrational alarm
communication in the
Damp-wood termite Zootermopsis nevadensis. Physiological Entomology 19:
187-190.
Mankin, R.W., W.L. Osbrink, F.M. Oi and J.B. Anderson. Acoustic detection of
termite infestations in urban trees. Journal of Economic Entomology 95:
981-988. |
|