Remarkably, aye-ayes are able to forage
using tap-scanning in acoustically
challenging and cluttered environ-
ments like the forests of Madagascar,
relying on their “bat-like pinnae” and
“finger-tapping” to detect grubs and
larvae deep beneath tree bark.
As evident, the aye-aye performs
tap testing in a highly specialized
manner, like the NDT/E techniques
used for composite material inspec-
tion, such as detecting disbonds. The
complex geometry of tree bark and the
composite-like structure of wood high-
light that the aye-aye’s process is highly
specialized, having evolved over millions
of years to be exceptionally efficient.
Recent studies by the author’s team
[34, 35, 36] demonstrate that the unique
shape of the aye-aye’s pinnae and the
mechanics of its auditory system play
a crucial role in filtering out unwanted
signals while enhancing sensitivity to
discontinuities, such as cavities, during
tap-scanning. The current tap-testing
technologies offer simple but effective
solutions in several applications such
as composite material inspection [37,
38, 39, 40]. However, they are limited
by low resolution, signal-to-noise ratio
(SNR), and depth of penetration in gen-
erating high frequency acoustic waves
in damped materials. Consequently,
they lack the capability to, as effectively
as aye-ayes, evaluate deep cavities in
composites. Utilizing the morphological
features of the aye-aye’s pinna and ear
canal to pioneer a new design for tap
testers can substantially enhance SNR
[34] and provide a hardware that can
filter out unwanted signals.
Given their extraordinary abilities,
the aye-aye truly deserves the title of
nature’s most fascinating NDE specialist.
2.2. Nature’s NDE Specialist #2:
Termites
Utilizing an exceptional tapping mech-
anism to generate acoustic waves,
aye-ayes rely on near-field acoustic cues
to detect and characterize cavities within
dry wood. Remarkably, even smaller
biological systems like damp-wood and
dry-wood termites exhibit similar vibro-
acoustic generation abilities. Termites,
small herbivorous social insects, are
well-known for their use of vibrational
signals and are inherently noisy biologi-
cal systems [41, 42, 43]. Vibrations caused
by body shaking, head drumming, and
chewing have been extensively docu-
mented [44, 45, 46, 47, 48, 49, 50]. In 1781,
Smeathman described the audible sound
produced by soldier termites during the
drumming process, referred to as “head
banging,” as a “signal of alarm” [51]. Two
distinct types of termite movements
have been identified: convulsive move-
ments, sometimes described as “cries”
without audible sound, which are used
to summon help, and head drumming
(head banging) (see Figure 3), in which
termites strike the ground with their
mandibles, producing audible “alarm
signals.”
Traditionally, termites have been
viewed as indiscriminate eaters.
However, recent studies suggest that
termites exhibit a clear ability to assess
the quality and potentially the thick-
ness of wood. Research has shown
that termites prefer blocks with higher
wood content [49, 52]. Wood, the
primary substance for dry-wood and
damp-wood termites, presents a wide
range of material properties, including
significant damping, making it difficult
to efficiently generate sound within or
from the material [53]. Given that worker
termites are blind, and chemical cues
alone cannot fully explain their selec-
tion process [54], recent studies indicate
that vibroacoustic cues serve as the
primary mechanism for wood charac-
terization. Recent findings show that
termites’ decision to consume specific
wood is influenced by vibroacoustic
signals, which are directly linked to the
material properties of the wood [52, 55,
56]. Howse demonstrated that substrate
vibrations caused by drumming (head
banging) or vertical oscillatory move-
ments can prompt continued behavior in
nearby termites that sense the vibrations.
This suggests that these vibroacoustic
signals may be used by termites to assess
wood in terms of thickness, quality, and
quantity of available food [44].
Despite their small size, termites are
capable of characterizing the thickness
of complex materials like wood and
evaluating how damp the wood is—
similar to how the modulus of elasticity
is assessed. This makes them a unique
biological system that can inspire the
development of combined robotics and
miniaturized NDT/E capabilities, par-
ticularly for applications where acces-
sibility is a challenge. Understanding
termites’ foraging behavior and the
influential factors, such as head shape
and dynamics, will enable engineers
to pioneer a miniature acoustic wave
generation mechanism inspired by the
exceptional vibroacoustic wave gener-
ation capabilities observed in termites.
This could lead to innovative small-scale
material characterization and inspection
processes.
2.3. Nature’s NDE Specialist #3:
Red and Arctic Foxes
Throughout evolution, species have
developed specialized acoustic sensory
systems to adapt to their ecological
niches. Arctic and red foxes, for example,
possess unique hearing abilities that
allow them to detect distant acoustic
sources underground or beneath snow
[57]. In winter, these fox species rely on
their extraordinary hearing to locate and
NDT TUTORIAL
|
BIOINSPIREDNDE
Figure 3. Zootermopsis nevadensis termite:
(a) soldier and worker and (b) soldier
drumming (head banging).
30
M AT E R I A L S E V A L U AT I O N • A P R I L 2 0 2 5

capture prey, such as lemmings, burrow-
ing under thick snowpack [58, 59]. The
exceptional acoustic sensing abilities of
these animals result from a combination
of external ears and coordinated motion
of the pinna, head, and body known as
head tilting (see Figure 4). This allows
for multitasking in binaural hearing
(acoustic sensing using only two ears).
However, limited research has been con-
ducted on how their external ears and
head-tilting strategies affect sound local-
ization in the acoustic field, particularly
when detecting low-amplitude sounds
beneath packed snow. The aye-aye and
termite perform active acoustic-based
testing, actively generating vibroacous-
tic cues to detect and characterize their
environment, while the fox engages in
passive acoustic-based foraging by lis-
tening to movements and noises during
its search for prey. One of the most
promising applications for such tasks is
underground leakage detection. Gaining
insights into this process could result in
the development of advanced noncon-
tact acoustic sensing technologies for
subsurface leakage inspections, using
binaural acoustic sensing. The funda-
mental principle of aeroacoustics leak
detection revolves around the generation
and propagation of sound waves when
gas escapes from a pipeline [60]. One
of the main drawbacks of this sensing
modality is its reduced sensitivity as the
sensors move further away from the
acoustic source due to significant atten-
uation [61]. Traditionally, an array of
microphones has been used to increase
the SNR and enable effective source
localization through beamforming tech-
niques [62]. However, this technique
generates a substantial amount of data,
which is not ideal for the development of
an automated leak detection platform as
well as a digital twin approach in infra-
structure monitoring. Fortunately, this
issue has been ingeniously addressed by
biological systems such as red and arctic
foxes utilizing only two ears (binaural
sensing). Instead of relying on an
increased number of sensors to enhance
sensitivity, these biological systems
evolved external ear (pinna) shapes to
act as hardware for amplifying sound
from specific directions, a capability
further complemented by the strategic
motion and control of the pinna and
head (e.g., head tilting). This approach
could revolutionize applications such as
leak detection or human localization in
rescue missions.
The three examples mentioned are
just a few among many species that
potentially perform processes similar to
NDT/E methods. Such bioinspiration
can lead to the development of new
technologies or the evolution of existing
ones, enhancing the reliability and sensi-
tivity of NDT/E methods.
2.4. Bioinspiration Impact on
NDT Education and Workforce
Development
One of the challenges we face as instruc-
tors and researchers in the field of
NDT/E is attracting students, as we often
compete with more visibly appealing
fields like robotics and data science,
which the younger generation perceives
as more attractive career paths. However,
bioinspiration offers a unique opportu-
nity to help attract students to the field
of NDT/E. The integration of bioinspired
concepts not only allows us to pioneer
new NDE technologies that can make
our world safer, but also serves as a
compelling tool to engage and attract
students. By highlighting the innovative
intersection between nature and tech-
nology, educators can increase student
involvement in NDT/E, bringing fresh
talent into the field and encouraging the
next generation of NDT/E professionals.
3. Conclusions
These three biological examples—
aye-ayes, termites, and foxes—are
among millions of species that use pro-
cesses remarkably similar to those we
conduct in the NDT/E fields. Through
evolution, these species have developed
highly specialized sensory systems for
survival processes such as foraging for
food, avoiding predators, and communi-
cating for mating. In many cases, these
functions are analogous to detecting
defects, characterizing materials, and
assessing environmental conditions—all
achieved without disrupting their sur-
roundings. By studying these biological
systems and in particular the processes,
for example tap-scanning, we can gain
valuable insights and inspiration for
advancing NDT technologies. The pre-
cision and efficiency seen in “nature’s
NDE specialists” offer promising avenues
for pioneering more adaptive, autono-
mous, and efficient NDT/E technologies,
particularly in challenging environments.
Furthermore, bioinspiration provides an
engaging platform for NDT/E education
and workforce development, attract-
ing younger generations to the field of
NDT/E and fostering the next wave of
innovation as well as keeping the world
a safer place to live.
As we continue to identify and
explore new “nature’s NDE special-
ists,” the potential for revolutionary
advancements in robotics, sensing,
and materials—specifically focused
on NDT/E and material characteriza-
tion processes—becomes increasingly
Figure 4. Red fox
head tilting.
A P R I L 2 0 2 5 • M AT E R I A L S E V A L U AT I O N 31
CREDIT:
KERRY
HARGROVE