Vision is a critical sense for most animals, allowing them to navigate their environments, find food, avoid predators, and communicate with others of their species. However, there are some animals that lack functional eyes or the ability to see at all. In this article, we will explore some of the animals that cannot see and discuss how they get by without vision.
Cave Animals
One of the most common environments to find animals without vision is in caves. Since caves lack sunlight, animals that live their entire lives underground have no need for functional eyes. Over generations living in total darkness, many cave-dwelling species have lost their eyes and vision altogether through the evolutionary processes of natural selection and genetic drift. Squ
| Animal | Description |
|---|---|
| Texas Blind Salamander | A blind salamander found in caves in Texas. It has rudimentary, non-functional eyes. |
| Olm | A blind salamander found in caves in Europe. It lacks pigment and has very small, sunken eyes. |
| Blind Cave Fish | A fish found in caves worldwide that lacks functional eyes. Some species do have non-functional vestigial eyes. |
Here are some examples of blind cave animals:
Adaptations
To navigate and find food without vision, cave animals have evolved other heightened senses:
- Touch – Many blind cave animals have very sensitive skin and whiskers to feel their way around.
- Smell – Cave animals often have a very acute sense of smell to locate food sources.
- Lateral line system – Special sense organs along the body can detect movement and vibration in water for blind fish.
- Echolocation – Some blind cave animals like bats use echolocation calls to map their environments.
Deep Sea Animals
Another environment devoid of light is the deep ocean. With very little sunlight filtering down past about 1000 meters, many animals that live exclusively in the midnight zone and deeper parts of the ocean also lack functional eyes.
| Animal | Description |
|---|---|
| Blind Shrimp | Shrimp species adapted to deep, dark waters usually have regressed or non-functional eyes. |
| Anglerfish | A deep sea predator that has extremely reduced vestigial eyes. They use a fishing lure to catch prey. |
| Gulper Eel | A bizarre eel with tiny non-functional eyes. They have huge jaws to swallow prey whole. |
Examples of blind deep sea species include:
Adaptations
Instead of vision, deep sea animals rely on the following to survive without light:
- Bioluminescence – Many animals produce their own light to attract prey, communicate, or illuminate their environment.
- Lateral line – Blind fish can detect movement and vibration in the water.
- Enhanced other senses – Touch, smell, and taste become more important in the absence of vision.
- Sit-and-wait hunting – Blind animals don’t need to see to catch sedentary or slow-moving prey.
Parasitic Animals
Parasites are organisms that live on or inside a host organism for prolonged periods, feeding off of the host. Many parasitic worms and other creatures live entirely inside their hosts with no exposure to light, so they have no need for functional eyes or vision. Examples include:
| Animal | Description |
|---|---|
| Tapeworms | Parasitic segmented worms that live in the intestines. They have no eyes or sensory organs. |
| Roundworms | Blind parasitic worms that absorb nutrients from the host’s gut. Can infect humans. |
| Copepods | Tiny blind crustaceans that are parasitic on fish and marine mammals. |
Adaptations
Parasites don’t rely on vision but have other adaptations to persist on their hosts, such as:
- Clinging mouthparts or bodies to attach to hosts.
- Chemical receptors to locate hosts and nutrients.
- Anaerobic metabolism to live without oxygen inside hosts.
- High reproduction rates to continually reinfect new hosts.
Fossorial Animals
Fossorial animals are those that spend most of their lives burrowing underground. Since they are constantly surrounded by soil and bedding material, there is no need for functional eyes. Examples of mostly blind fossorial animals include:
| Animal | Description |
|---|---|
| Moles | Have very small eyes to keep dirt out while digging. Rely on touch, smell, and hearing underground. |
| Marsupial moles | Blind mole-like marsupials native to Australia. Have only vestigial non-functional eyes. |
| Blind snakes | Burrowing snakes with reduced eyes adapted to a life underground. |
Adaptations
To thrive underground without sight, fossorial creatures have evolved:
- Powerful digging claws, tails, heads, and limbs.
- Sensitive whiskers and touch receptors.
- Keen sense of smell to locate food.
- Heat sensitivity to find prey.
Caveats
While the animals we’ve discussed rely primarily on senses other than vision to survive, a few caveats are worth mentioning:
- Many are not completely blind, but rather have varying degrees of reduced vision.
- A number of cave species have eyes that still detect light for circadian rhythms.
- Parasites and fossorial animals may have larval stages with eyes.
- Eyes may serve non-visual functions like protecting the brain or sensing pressure.
So while these animals are blind for all intents and purposes, vestigial eye structures can still serve important functions other than seeing.
Conclusion
In summary, animals without vision tend to inhabit environments devoid of light where eyes would be useless. These include caves, the deep sea, inside hosts as parasites, and underground as burrowers. To navigate and survive without sight, blind animals have enhanced other senses such as smell, touch, and hearing. Non-visual cues like vibrations and chemical signals become essential. While not completely blind, animals in dark environments display a remarkable ability to adapt and thrive in the absence of vision.