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This is the fifth of a series of blogs on the subject of alien and monster biology. The first, which covers respiration, can be found here.

All living things respond to stimuli. These stimuli can take many forms, but include:

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A rabbit with big ears
  • Sound

As a general rule, if an animal is reliant on a particular sense, the organ used to detect this will increase in size e.g. creatures who are focused on sound have big ears. The obvious examples we see in the UK are rabbits and hares, but the size of elephants’ ears would suggest that sound is important to them (although there may also be some heat exchange considerations.

The range or frequency of sounds that can be heard by different species varies; dogs can hear in a range that humans would characterise as ultrasound i.e. the ‘silent’ dog whistles (23–54Hz). The human ear detects sounds at a frequency of 15–20Hz.

Sound is also important to aquatic creatures such as whales who use sonar (10–40Hz)as well as audible sound. Sound travels faster and farther in water than air, so detecting it is highly useful. I was initially dubious about the physics of this claim, but it is explicable because water molecules are closer together than air molecules. This means it is easier to transmit sound (or energy) between those molecules, which seems to make sense. Thinking about other life forms; in theory an animal with very advanced hearing could use sonar type senses on land, especially if the atmosphere on their home planet was thicker or denser that on earth.

Bats use much higher frequencies (100Hz) to use echolocation in air. Elephants can sense low frequency noises made by other elephants miles away through their trunks and their feet. They can tell the difference between individuals and use subtle differences in what each foot feels to triangulate the source.


Animals who are used to nocturnal activities, or live in dark caves often have very sensitive (and enlarged) eyes e.g. bush babies. Incidentally, these give the appearance of a vulnerable creature; they resemble human babies, so we are programmed to find them cute. This is why Disney Princesses and animé characters are drawn in the way they are; they appeal to our inbuilt tendency to protect and nurture. Not all of the creatures who look like this are vulnerable e.g.the Slow Loris has glands on the side of their elbows which secrete a deadly toxin. Woe betide anyone who picks them up for a cuddle!

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Guinea pigs — a prey species with laterally sited eyes

Where the eyes are sited on the head depends on the type of animal e.g. prey species have wide angled, laterally focused eyes, whereas hunters have narrow angle, forward pointed eyes. This means predators are better able to chase and follow prey, whereas those creatures who are likely to be hunted can see things creeping up on them.

The four-eyed fish has only 2 eyes, but they are modified in a way that allows them to see above and below water at the same time. Spiders generally have 8 eyes (although some may only have 6) with different eyes performing different functions. Some of them are sensitive to the UV spectrum, others are more receptive to movement, allowing them to better chase prey.

Some snakes, such a pit vipers, boas and pythons can see in infrared, with heat sensors along their upper and lower jaws. These pits act like a pair of eyes that only see infrared light, which humans feel as heat. The pits aren’t focused well enough for the snake to pinpoint prey without visual help, but they’re so sensitive that they can notice temperature variations of as little as a thousandth of a degree.

Some animals see colours less clearly than people, or fewer colours, so it’s entirely possible that alien species could be ‘blind’ to certain colours or patterns.

Animals such as cats and dogs have a reflective area the tapetum lucidum on the back of the eye which reflects light at low light levels, allowing better sight in low light. This is what makes cats eyes reflective when you catch them in headlights or with a torch.

Certain creatures can also see polarised light; the up and down or side to side oscillations that light waves make as they travel. The octopus has patterns on its skin which are only visible if you can see differences in polarised light, as the eyes of an octopus can. Mantis shrimps can see circular polarisation of light, which they use to signal other shrimp. In this way aliens could


The external surface of most animals and birds is sensitive to touch. This is taken to extremes in the whiskers of felines, where enlarged and specialised hairs are used as touch sensors. They are not the same as the hairs on the rest of the body, being thicker and more deeply attached. They are used to sense by touch and are particularly important when cats are too close to the prey to see it. Muscles pull them forward so that cats know when to pounce/bite.

These whiskers can also be seen on cats’ front legs. Other mammals such as dogs also have them, as do aquatic creatures such as seals.

Fish make use of similar tiny hair cells in the lateral line system, which runs the length of the body sensing vibrations through the water. This can be used to track prey.

Magnetic Spectrum

Some animals appear to be able to sense the magnetic spectrum. Bees can do this although scientists have not worked out how. It is suggested that there may be that there are north aligned cells in the bees’ abdomen, or that sunlight sets off a chemical field. Magnetic senses have also been shown to work for animals as diverse as homing pigeons, mice and drosophila fruit flies.

Worms use this sense to tunnel. 1mm long roundworms rely on a single nerve for their whole body, but this can detect the earth’s magnetic field. The worms have been studied heavily by scientists, but the magnetic sense was not unknown until a Texan lab noticed that the worms they had ordered from Australia were burrowing in the wrong direction.

Could this mean we may have races of explorers who cannot get lost?


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Bee on a quince flower

Bees use voltage — they build up a positive charge as they fly and flowers are negatively charged, meaning that bees can detect if another bee has just collected from that flower.

Sharks also use electrical conductivity to detect food. Lorenzini jelly fills a network of pores around the shark’s face and can detect the electrical charge of other animals relative to the water around them, even in very murky water.

Imagine an alien race which could detect electrical flows just by being in the vicinity of a machine; wouldn’t they make excellent engineers?

Smell and Taste

Smell and taste are closely linked and animals are generally far more sensitive in their smell and taste sensations than we are.

Everyone hates a phlebotomist who keeps poking away in search of a vein. Vampire bats avoid this by sniffing out veins using the same TRPV1 proteins that tell you that your tea is scalding hot. Instead of alerting them to danger, these proteins — concentrated in a bat’s nose — tell them when they’re above skin warmer than about 86 ℉, where there’s a big, juicy blood vessel hiding underneath. This means they know where to bite.

Located in the the vomeronasal organ (located in the nasal chamber) allows animals to deter pheromones. Pheromones are secreted in a variety of circumstances and may be used to make young feel safe and secure or can be sex-signaling compounds which tell the animal if a potential mate is receptive. Humans have this organ but it is not believed to be functional. Imagine how much easier dating would be if it worked! It is reported that pheromones to make people feel happy have been used in shops to encourage people to linger and spend money.

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This is the fifth of a series of blog posts, which have been derived from a lecture I gave at Right on Paper, a one day conference of academic talks on various subjects, for speculative fiction writers, held in London on 3rd February 2018.

This talk, was in turn sparked by a conversation in the bar at Nine Worlds, a science fiction and fantasy convention, where I announced that there was a really interesting talk which could be given on Xenobiology and decided I’d better put my money where my mouth was.

I also blog on veterinary matters here.

Written by

Vet, likes all things animal. Roleplayer, LARP & Crooked House LRP. Plays and organises interactive narrative fiction. Travels as Vetvoyages.

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