Scientists are deciphering the mystery of the lobsters amazing sense
of smell. What theyve learned is helping them to build
bomb-sniffing underwater robots.
Lobsters are shy, sneaky creatures. During the day, they
hide in safe dens and crevices in coral reefs, preferring
only the company of their fellow buddies and mates. But at
night, the spine-covered critters leave their shelters to
roam and hunt. A pair of hairy antennae guides them through
a rich world of scentsof yummy clams, delicious fish,
or delectable black musselseven in absolute darkness.
The lobster rhythmically swings its "noses" up and down
through the water, catching the faintest smells from
predator or prey.
More than 20 years ago, neurobiologists showed that the
lobster's brain detects scent only while it flicks its
antennae. New studies now reveal exactly how these flicks
are responsible for the lobster's marvelous sense of smell.
The research, based at the University of California at
Berkeley, and Stanford University, is part of a joint
effort at several institutions funded, surprisingly, by the
U.S. Navy. The military is involved for one reason: It
wants better robots for detecting underwater mines or
monitoring toxic waste. And the crustaceans can show the
Navy the way.
"If you want to build unmanned vehicles or robots that
go into toxic sites, and you want those robots to locate
something by smell, you need to design noses for them,"
says UC Berkeley researcher Mimi Koehl. It just so happens
there is no better nose to imitate than the lobster's
schnoz, which has had plenty of time to improve over
millions of years of evolution. Engineers and biologists
are teaming up to learn and steal from designs that nature
worked out long ago, a field called biomimetics. Lobsters
are not only master sniffers, but they've also adapted
nicely to the rough conditions of surf break zones without
getting washed away. Both features are crucial for
underwater robots to succeed in hazardous coastal
Koehl, a biomechanical engineer, wants to understand
how the lobster's nose masters the challenge of smelling
underwater. On a recent afternoon in her lab, she explained
her work. "Most biomechanics researchers are the guys who
develop running shoes or artificial knee joints. But some
of us straddle biology and ask questions about non-human
Like an aerodynamics engineer studying the flow of air
over the wings of an airplane, Koehl looks at the flow of
water and odor molecules over the pair of antennae attached
to the lobster's head. This flow brings odor molecules into
contact with sensory receptors in each "nose." Unlike in
mammals, where smelly molecules stream into the nostrils
with every breath of air, lobsters must move their antennae
to "sniff" smells dispersed in turbulent water.
Each antenna is about two inches long and splits into a
Y-shaped structure with two pointy tips"hairy little
legs," is how Koehl tenderly describes them. Peering
closely through a magnifying glass at one of these antenna
tips, she glimpses a dense zone of hair tufts staggered in
a zigzag arrangement. It looks like a miniature toothbrush.
Each hair is covered with multiple nerve cells that can
detect odors. Along the edges of the toothbrush, larger
hairs line up like a long alley of tree trunks. Up to five
times thicker and taller than the smallest hairs, these
hairs control the flow of odor molecules and water to the
shorter, inner sensory hairs. For that reason, researchers
call them "guard hairs."
"To understand the physics of smelling," Koehl says,
"you need to understand the fluid dynamics of water
interacting with hairs." She holds up a scaled-up plastic
model of the toothbrush-like array of sensory and guard
hairs. "If you look at the array of hairs, it is full of
holes," she says, poking her fingers into the spaces
between the taller guard hairs. Nonetheless, water can't
normally flow through these gaps; instead, it takes the
path of least resistance and flows around the hairs. It is
only when the entire, hairy array is moving fast
enoughwhen the antenna is flickedthat water can
flow through the guard hairs. Then, sensory hairs can
encounter odor molecules and transmit the scent information
to the lobster's brain.
To observe the flow of odors, Koehl uses another
plastic model that's about 300 times bigger than the
lobster's microscopic guard hairs. She places the model,
mounted on a small motorized cart inside a large glass
tank. To approximate the drag that occurs when seawater
flows through such teeny hairs, Koehl's tank is filled with
gluey Karo corn syrup. She adds tiny little red beads that
float in the sticky sweetener, like odor molecules in
water. Moving the plastic model at various speeds through
the syrup creates a flow of the red beads across the guard
hairs. Koehl records it all with a video camera.
At slow speeds, the beads merely drift around the guard
hairs. But as the speed picks up, the hairs get leaky and
let the beads pass through. "Models are powerful tools. You
can systematically dissect and understand what role each
part has," Koehl says with satisfaction. "With organisms,
nature never does that for you."
Koehl's work has established the role of guard hairs as
selective gates. Based on her experiments, she predicted a
double role for the lobster's antennae: When flicked
downward, they act as sieves that trap odor molecules. But
when slowly moved back up, the antennae behave more like
paddles, pushing water and odors away.
Much like cigarette smoke in the air, traces of scent
released by fresh fish form a constantly changing cloud, or
plume, in the water. A lobster trawling for dinner is never
aware of this full cloud. It senses only tiny slices of the
plume from flicking its hairy antennae repeatedly. These
series of flicks through odor plumes fascinate Jeff Koseff,
an environmental fluid mechanics engineer at Stanford.
Using laser technology, Koseff has developed a method
to dissect the plume's structure. In lab experiments, he
mixes odor molecules with a special invisible dye into
water in a tank. Then he aims a thin sheet of laser light
(rather than just a single beam) into the tank,
illuminating one slice of the odor cloud. Dye molecules
within this laser-lit slice give off fluorescent light,
allowing Koseff to record the cross-section with a
videocamera. In the resulting image, the dye molecules look
like fine, threadlike filaments swirling about, reminiscent
of the pattern of an oil slick on the surface of a pond.
The picture gives Koseff an idea of what the lobster smells
while flicking its antenna.
To find out more, working with Koehl, Koseff built a
simple robot out of a molted lobster shell filled with
plastic. They added this mechanical creature to his
experiment, positioning one antenna to move within the
sheet of laser light. With the camera, they recorded which
parts of the thin filaments of dye penetrated the hairy
brushes on the tips of the antenna. "It's a bit like
placing toothpaste on a toothbrush," Koehl says.
For the first time, the scientists could measure what
the lobster encounters with each flick. Their results
showed that during the upstroke, when guard hairs push
seawater away, the odor filaments retain the original shape
with which they first entered the sensory brush. The next
flick, downward, breaks up the filaments as the antenna
captures scent molecules from the water. It stores the odor
sample for about a tenth of a secondjust long enough
for sensory neurons to detect the smell, even as the
antenna is already swinging upward again. On the next
downstroke, the stored odor is replaced by a new scent
sample. Each flick is like a deep sniff supplying new
Together with a neurobiologist in Florida, Koehl and
Koseff are now working on combining electrical recordings
of the lobster's brain with realtime imaging of the
plume structure. If successful, they'll see what smells the
antenna is picking up and what the lobster's brain is
SCIENTISTS ELSEWHERE ARE WORKING on other parts that
lobster-inspired robots will need. Underwater devices
programmed to autonomously sniff out explosive underwater
mines or toxic waste sites require some intelligence. And
they need to navigate sand, stones, and rubble on the
bottom of the sea. Two other research efforts are focusing
on these goals.
At the Marine Biological Laboratory in Woods Hole, Massachusetts,
neurobiologist Frank Grasso and his team has designed a robot to study
lobsters' behavior in response to clouds of scent. RoboLobster, as it's
called, doesn't actually look much like a crustacean. It's a
twowheeled vehicle about 30 centimeters long, featuring two smell
sensors in the front and instruments to gauge its position. But its body
size and shape are copied from the real animal, as are its speed, pattern
locomotion, and the way its sensors are arranged.
Grasso can program the way RoboLobster reacts to the
fishy odor plumes it senses. In a typical experiment, he
exposes a live lobster and the robot to the same
conditions. Based on the differences in how they respond,
he finetunes RoboLobster's programming to better mimic
natural lobster behavior.
Grasso and RoboLobster recently returned from a field
trip to the bottom of the Red Sea off Israel, where he
exposed his baby to its first real-world test. A team of
frogmen swum out and covered a portion of the sea floor
with long sheets of linoleum so that RoboLobster wouldn't
get stuck on pieces of coral or other obstacles. The
frogmen then escorted the robot three meters underwater,
generated a colored odor plumeand let it roll. It was
the first time the mechanical crustacean was exposed to the
turbulence of naturally occurring waves, but it behaved
just as it did in the lab: As soon as odor molecules
reached RoboLobster's nose, the vehicle started moving
towards the source of the scent.
For Grasso, it was a terribly exciting moment, to see
his invention working in the environment that originally
inspired its design. "I felt like a real Indiana
Jones-kind-of-scientist," he says with a grin.
While RoboLobster is good at sniffing out plumes,
another of its brethren is proving to be a versatile
roamer. In just five years, neuroscientist and engineer Joe
Ayers and his team at Northeastern University in Boston
have constructed a fully biomimetic lobster robot. Even
without seeing the robot in action, a viewer of the
eight-legged metallic critter has no doubt of its heritage.
With its thin legs, two front claws, and a long tail, this
vehicle has all the key anatomical features of a lobster.
Ayers built in these features not for their natural appeal,
but for their function. The claws and the tail, for
instance, stabilize the robot while it crawls along the
bumpy sea floor.
Within the mechanical lobster sits an electronic
"brain" inspired by Ayers' early graduate work at the
University of California at Santa Cruz. As a trained
neurophysiologist, he's deciphered all the nerve cells in
the center of the lobster brain that produce the
crustacean's pattern of locomotion. To build the controller
that steers his robot, Ayers created a computer model based
on these neurophysiological measurements. This artificial
nervous system can command the robot to move in all
directions exactly like using feedback from the lobster's
own walking patterns. "What is really unique," Ayers says,
"is that the robotic lobster can change its walking
behavior on a step by step basis."
Ayers and his team recently finished building the
second generation of the robot. This version can walk
entirely on its own, and without the cable support that its
predecessor needed. Compact battery packs provide enough
energy to keep it going for several hours. Some sensors
help stabilize the metallic critter's balance, while others
that detect touching and bumping guide it around obstacles.
From a base station, Ayers can send directional commands to
the robot via sonar communication. He even designed the
vehicle so that additional instruments such as cameras can
be mounted on the back of its tail.
Though Ayers' efforts were fully focused on creating a
robot capable of running on the sea floor to hunt for
underwater mines, his invention currently lacks a nose for
TNT or any other explosives. Yet he says with confidence,
"If the Navy combines Grasso's RoboLobster with our robotic
lobster, they will completely solve their problem."
What the Navy wants is a robot that can track
explosives in the 30-meter zone off a shoreline. "We think
that a legged walker that can search would be the ideal
device on the rocky bottom of a surf zone," says Joel
Davis, the research coordinator from the Office of Naval
Research. Loaded with a camera and explosives, a robotic
lobster would search for mines along an area enclosed by
sonar buoys. Upon finding a suspicious object, it would
transmit an image to a human operator, who could identify
whether it had found a real mineand trigger the robot
to explode to get rid of the threat. At $300 a pop, the
Navy's self-destructing robotic lobsters would be a cheap
way to make seashore operations safer.
Meanwhile, Ayers is turning his attention to biological
challenges in robot design. Just like Grasso, he hopes to
do real-world experiments exposing his creature to the
lobster's original habitats. One day, these robotic
lobsters may even start to invade the dens of their natural
compadres. "Ultimately," Ayers muses, "our robotic lobster
should be able to do all these things a real lobster
doesexcept have sex."