|Some animals have developed amazing adaptations to their
environments. Many different types of energy exist in the environment,
some of which humans cannot detect. Here are some examples of how some
animals sense the outside world and the anatomical structures that allow
them to do so.|
- Can detect small movement through 5 cm of earth.
- Can see polarized light.
- Can detect warmth of an animal from about 16 cm away using its
- Bats can also find food (insects) up to 18 ft. away and
get information about the type of insect using their sense of
- Can hear frequencies between 3,000 and 120,000 Hz.
- Can see light between wavelengths 300 nm and 650 nm.
- Have chemoreceptors (taste
receptors) on their jaws, forelimbs and antennae.
- Worker honey bees have 5,500 lenses ("ommatidia") in each eye.
- Worker honey bees have a ring of iron oxide ("magnetite") in their
abdomens that may be used to detect magnetic fields. They may use this
ability to detect changes in the earth's magnetic field and use it for
- Can see polarized light.
- Has chemoreceptors (taste receptors)
on its feet.
- The butterfly has hairs on its wings to detect changes in air
- Using vision, the butterfly Colias can distinguish two points
separated by as little as 30 microns. (Humans can distinuguish two points
separated by 100 microns.)
- Retina has 1 million photoreceptors
per sq. mm.
- Can see small rodents from a height of 15,000 ft.
- Has hearing range between 100 and 60,000 Hz.
- Olfactory membrane about 14 sq. cm. For comparison, humans have
an olfactory membrane of about 4 sq. cm.
- The eyes of the chameleon can move independently. Therefore,
it can see in two different directions at the same time.
- Can detect movement as small as 2,000 times the diameter of a
- Has hairs on claws and other parts of the body to detect water
current and vibration.
- Many crabs have their eyes on the end of stalks.
- Has sensory hairs that can detect movement of 0.1 microns (at
100 Hz frequency).
- Can hear using their legs; sound waves vibrate a thin membrane on
the cricket's front legs.
- Has olfactory membrane up to 150 sq. cm.
- Can hear sound as high as 40,000 Hz.
- Like bats, dolphins use echolocation for movement and locating
- Can hear frequencies up to at least 100,000 Hz.
- Eye contains 30,000 lenses.
- Entire body covered with chemoreceptors
- Eyeball length = 35 mm (human eyeball length = 24 mm)
- Visual acuity is 2.0 to 3.6 times better (depending on the type of
eagel) than that of humans. (Shlaer, R., An eagle's eye:
quality of the retinal image, Science, 176:920-922, 1972.)
- Has hearing range between 1 and 20,000 Hz. The very low frequency
sounds are in the "infrasound" range. Humans cannot hear sounds in the
- Can see a 10 cm. object from a distance of 1.5 km.
- Visual acuity is 2.6 times better than human. (Garcia et al., Falcon visual acuity, Science, 192:263-265,
- Can see sharp images even when diving at 100 miles/hr.
- Some can detect the L-serine (a chemical found in the skin of
mammals) diluted to 1 part per billion.
- Have a "lateral line" system consisting of sense organs
in canals along the head and trunk. These receptors are used to detect
changes in water pressure and may be used to locate prey and aid
- Some fish can see into the infrared wavelength of the
- Has 3 or 4 pairs of whiskers, called barbels, to find food. The catfish also has approximately
100,000 taste buds. (Humans have only 10,000 taste buds.)
- Only have rods in the retina: 25 million rods/sq. mm. Perhaps
they need this high density of photoreceptors to detect the dim
biolumninescence that exists in the ocean depths.
- Collects underwater sound vibrations with an air bladder. The
signals are then sent from the air bladder to the "weberian apparatus" in
the middle ear and then to the inner ear. Hair cells in the inner ear
respond to the vibration and transmit sound information to the fish
Fish ("Four-eyed Fish"
- Can see in air and water
simultaneously. Each eye is divided by flaps, so there is one opening in
the air and one in the water.
- Each eye has 3,000 lenses. (Simmons and Young, 1999)
- Eye has a flicker fusion rate of 300/sec. Humans have a flicker
fusion rate of only 60/sec in bright light and 24/sec in dim light. The
flicker fusion rate is the frequency with which the "flicker" of an image
cannot be distinguished as an individual event. Like the frame of a
movie...if you slowed it down, you would see individual frames. Speed it
up and you see a constantly moving image.
- The small parasitic fly (Ormia ochracea) can locate sounds
within a range of only 2o of the midline. (Mason et al.,
Nature, 410:686-690, 2001)
- Blowflies taste with 3,000 sensory hairs on their feet.
an eardrum (tympanic membrane) on the outside of the body behind the
- Eye is 25 cm in diameter.
Retina can contain up to 1 billion photoreceptors.
- Has hairs ("sensilla") all over the body to detect air
- Can hear up to 50,000 Hz.
- Normal vision for people is 20/20. A hawk's vision is equivalent
to 20/5. This means that the hawk can see from 20 feet what most people
can see from 5 feet. (Scientific American, April 2001, page
- Has 1 million photoreceptor per square millimeter in its
- Able to detect the temperature of sand within 2 degrees F. This
temperature is needed for the iguana to lay its eggs.
- Can hear frequencies between 1,000 and 100,000 Hz. By
comparison, humans can hear frequencies between 20 and 20,000
- Uses its fleshy star nose for hunting. The
Star-nosed mole has
100,000 nerve fibers that run from star to the brain. This is almost six
times more than the touch receptors in the human hand.
- Attracted to host by human body odor (especially foot odor),
carbon dioxide, body heat and body humidity.
- Noctuid Moth has a hearing range between 1,000 and 240,000
- Emperor Moth can detect pheromones up to 5 km. distant.
- Silkworm Moth can detect pheromones up to 11 km. distant.
This moth can detect pheromones in concentrations as low as 1
molecule of pheromone per 1017 molecules of air. A receptor
cell can respond to a single molecule of the pheromone called bombykol and
200 molecules can cause a behavioral response.
- Retina contains 20 million photoreceptors.
- The eye has a flicker fusion frequency of 70/sec in bright
The pupil of the eye is rectangular.
Has chemoreceptors (taste
receptors) on the suckers of their tentacles. By tasting this way, an
octopus does not have to leave the safety of its home.
a flat cornea that allows for clear vision underwater. Penguins can also
see into the ultraviolet range of the electromagnetic
- Tongue contains 15,000 taste buds. For comparison, the human
tongue has 9,000 taste buds.
- With eyes mounted laterally on their heads, pigeons can view 340
degrees...everywhere except in back of their heads.
- Can detect sounds as low as 0.1 Hz.
- Has electric sensors in its bill that can detect 0.05 microvolts.
Other receptors in the bill are for touch and temperature
- The cochlea of the inner ear is coiled only a quarter of a
turn. In man, the cochlea is coiled about 2.7 times.
- Tongue contains 17,000 taste buds.
- Has hearing range between 1,000 and 90,000 Hz.
- Each eye can move independently.
100 eyes around the edge of the shell. These eyes are probably used to
detect shadows of predators such as the starfish.
- Can detect air moving at only 0.072 km/hr with special hairs on
- Can have as many as 12 eyes.
The last three facts are from D.Perrine, Sharks
and Rays of the World, Stillwater: Voyaguer Press, 1999.
- Has specialized electrosensing receptors with thresholds as low as
0.005 uV/cm. These receptors may be used to locate prey. The dogfish
can detect a flounder that is buried under the sand and emitting 4
uAmp of current.
- Some sharks can detect fish extracts as concentrations lower than one
part in 10 billion.
- Some sharks sense light directly through the skull by the pineal body.
- The thresher shark has an eye up to 5 inches (12.5 cm) in diameter.
- Pit-vipers have a heat-sensitive organ
between the eyes and the
nostrils about 0.5 cm deep. This organ has a membrane containing 7,000
nerve endings that respond to temperature changes as small as 0.002-0.003
degrees centigrade. A rattlesnake can detect a mouse 40 cm away if the
mouse is 10 degrees centigrade above the outside temperature.
- The tongue of snakes has no taste buds. Instead,
the tongue is used to bring smells and tastes into the mouth. Smells and
tastes are then detected in two pits, called "Jacobson's organs", on the
roof of their mouths. Receptors in the pits then transmit smell and taste
information to the brain.
- Snakes have no external ears. Therefore, they do not hear the music
of a "snake charmer". Instead, they are probably responding to the
movements of the snake charmer and the flute. However, sound waves may
travel through bones in their heads to the middle ear.
- Snakes have no moveable eyelids. Instead, they have a clear,
scale-like membrane covering the eye.
- Retina has 400,000 photoreceptors per sq. mm.
- Many spiders have eight eyes.
- Arms covered with light sensitive cells. Light that projects on
an "eyespot" on each arm causes the arm to move.