Animal Senses
D. Indumathi, The Institute of Mathematical Sciences, Chennai

We know that we have five senses, such as sight, sound, smell, touch, taste. Some animals are sensitive to even more kinds of stimulus than we are. For instance, apart from sight, touch, and sound, animals are sensitive to temperature, gravity, electric fields, and even to lights and sounds that we are not sensitive to, such as ultraviolet light and ultrasound.
Here are some amazing adaptations of animals.

Rabbits
The average person has about 10,000 taste buds and they're replaced every 2 weeks or so. But a rabbit tongue contains 17,000 taste buds situated both in the mouth and pharynx. They can distinguish between sweet, sour, bitter and salty. In the wild, rabbits can also differentiate between toxic and non-toxic plants.
Rabbits have over fifty million receptor cells in their nose, compared to our meagre six million. These enable rabbits to smell predators well before they may even see them.
Hearing is a rabbit’s most vital sense, hence the large upright ears. They can also detect much higher pitched sounds than we can. The auditory system is used to detect predators, as well as to help a rabbit perceive the area around him. Most rabbits have large, erect ears. When alert, the ears move forward and backward as they attempt to pinpoint the danger. When the rabbit is relaxed, the ears lie along the back, but they are quite responsive to noise.
Rabbits have whiskers that are as long as the body is wide. These help in measuring the width of openings and passages in the dark. The whiskers are located on the mouth, nose, and cheeks and above the eyes. There are sensory nerves located at the follicle end of each whisker. The entire body also has nerve endings that are sensitive to touch. So always be gentle when handling rabbits.
Chameleons
All of us know that chameleons can change colour. They are born with special cells (under the skin) that have a colour or pigment in them, called chromatophores. The top layers of chromatophores have red or yellow pigment. The lower layers have blue or white pigment. When these pigment cells change, the chameleon’s skin colour changes.
But what you may not have known is that the eyes of the chameleon can move independently. Therefore, it can see in two different directions at the same time! This kind of ability provides it with approximately 360-degree vision. 
The eyes of the chameleons are actually made up from one large cone shaped eye lid which almost covers the whole eye. So, their upper and lower eyelids are joined, leaving a tiny hole to expose the pupil. The chameleon can then watch a predator coming its way, and at the same time, examine its surroundings for the best escape routes.
One of the most striking features of the chameleon eye is the presence of the concave lens. Humans have convex lenses that focus the image on the retina. The combination of concave lense and convex cornea gives them incredible eye sight. In fact, the chameleon eyes are considered to have the highest image magnification among many other vertebrate’s eyes. Their eyes focus extremely quickly.
When the chameleon spots prey such as a cricket which can be as much as 10 meters away, it turns its head to face the prey. It then points both eyes directly at the target, switching to stereoscopic or binocular vision. The chameleon uses its binocular vision to increase depth perception and helps the chameleon to aim with pin point accuracy. Combine that with a long tongue, and you can ensure yourself a great meal every time.

Earthworms
Earthworms do not possess eyes; instead they have light receptors that detect when it is light or dark. This is useful to avoid predators and know when it is safe to search for food and to avoid drying out in sunlight. Earthworms have no ears, but can sense vibrations.
The skin performs most of the usual functions in earthworms. Earthworms don’t have a sense of smell or a nose, but they do have to breathe! Earthworms breathe by absorbing oxygen through their skin. Air dissolves on the mucus of their skin, so they must stay moist to breathe. If worms dry out, they suffocate.
Worms have sense organs in the front end of their body which help them find food.
Tiny sensory organs cover worms' bodies and provide their sense of taste. These organs are called chemoreceptors, and they help worms detect chemical sensations, which translate into taste reception. Worms also use these chemoreceptors to smell the air and their potential food source. They are tiny sense organs which detect chemicals in the soil. The muscles make movements in response to touch and taste.

Ants
Ants have been around since the time of dinosaurs. Probably all of you know that they have the ability to carry between 10 and 50 times their own body weight! But they have other amazing senses as well.
Due to their small size, ants don’t have the room to accommodate a complex respiratory system such as ours. Instead, they breathe in oxygen through spiracles which are a series of holes located around the sides of their bodies. The spiracles are connected through a network of tubes which help distribute the oxygen to almost every cell in their body. The released carbon dioxide exits through the same tubes.
Ants don’t have ears. They use vibrations to hear, using it when foraging for food or as an alarm signal. They use the vibrations in the ground to hear by picking them up in the subgenual organ which is located below the knee.
Ants have two stomachs, and it’s not because they are greedy. One of their stomachs is for holding food for their own consumption, whilst the second one is to hold food to be shared with other ants. This process is known as trophallaxis and allows a colony to work extremely efficiently. It allows for the ants who forage for food to feed those which stay behind and tend to the duties of the queen and the nest.
They have a great sense of smell (they always find the chocolates in the house!) actually have four to five times more odour receptors (located on their antennae) than most other insects. It’s this exceptional sense of smell as well as a keen memory that helps ants find food.
When worker ants leave their nest to search for food, they leave behind a trail of pheromones (chemical scents) — like leaving a trail of breadcrumbs to help you find your way home. After an ant finds food, it turns around and follows a different pheromone trail back to the nest. While it travels home, it lays down more pheromone on the trail, reinforcing the trail. When other worker ants come across the pheromone trail, they may abandon their own random search for food to follow the pheromone trail directly to the food source.
On this first trip, the ant stores images of the route. On later trips back to the same food source, the ants use landmarks and memories of the whole landscape to find their way. The ants use different landmark memories on their way to and from the food site. Some ants can store many memories and activate the correct ones as needed.

I'm sure we would have been delighted if we had some of these senses!

Adapted from Neuroscience For Kids - Animal Senses