TECHNICAL | PPC109 October 2022

Rats are fascinating. We spend so much of our time around them, chasing them and tracking them, but when was the last time you stopped to truly watch them, in order to appreciate how, or even why, they act in the way that they do?

In this article, Alex Wade from Wade Environmental delves into some of the incredible (and sometimes disgusting) things rats can do. 

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Rats are by far and away one of the most adaptable animals on the planet. Despite having the individual intellectual capacity of half a spinach sandwich, they are collectively a veritable powerhouse of problem solving and tenacity.

Individually rats may not rate too highly, despite being able to demonstrate tenacious problem-solving skills – but collectively they enhance these skills to powerhouse level.

What is it that makes them such perilously persistent pests? Well, it’s some of the incredible adaptations they have developed that have allowed them to survive alongside mankind for such a long time.

We will have a look at a few of these adaptations over the next couple of pages; adaptations that are totally incomprehensible to us, but utterly extraordinary to rodents.

“...we have mice creating urine pillars and rats defecating in discrete latrines.”

Follow your nose

Humans have one sense of smell, and it is relatively limited. 

Granted we are acutely aware when we have stepped in something decidedly unpleasant, or we might be pleasantly surprised at a new perfume. 

And that is largely where it ends. We certainly don’t use our sense of smell to make complicated choices, plot intricate navigational routes or to ascertain the age, sex or fertility of other humans... at least I hope you don’t!

Yet these are some of the things that a rat is able to achieve with its nose and this is because rats have two unique senses of ‘smell’. 

The first sense is much like our own but vastly more powerful.

Indeed, the chemoreceptors within a rodent’s nose directly correlate to specific regions within their brains, meaning when they experience a scent they aren’t necessarily associating it with a memory, but with a detailed image map concocted through the chemical analysis of that smell. 

We certainly don’t use our sense of smell to make complicated choices, plot intricate navigational routes or to ascertain the age, sex or fertility of other humans... at least I hope you don’t!

Alex Wade, Wade Environmental

This means that they are able to pick up the most minute of scents, as well as being able to distinguish between smells that to us would be utterly alike. 

This heightened sense of smell really comes to the fore when you consider the fact that rodents are primarily operating in low (to zero) light environments, in addition to having outrageously awful eyesight, resulting in a feature of the rat which is likely to be providing the bulk of a rat’s navigational drive and exploratory behaviour.

The second mechanism of ‘smell’ is provided by a structure called the vomeronasal organ. 

This allows rodents to detect both proteins and pheromones, with the combination of these in a single ‘scent’ able to convey a stunning range of complicated information. 

And where would evolution deign to secrete these informational markers? Well, in urine, naturally.

It is, in fact, the reason we have mice creating urine pillars and rats defecating in discrete latrines.

Time to dispel a common myth: far from having weak bladders or defecating simply when the mood takes them, rats and mice will use these eliminatory events to leave behind a messenger board of information, such as their age, sex, health, social status and even individual recognition.

Next time you see a urine pillar or a latrine pile, think to yourself: that crap is rat Twitter.

Winning by a hair

Now, if having a highly-sensitive schnoz isn’t super power enough, consider the rat’s whiskers. 

Unlike our own ‘whiskers’, the whiskers of rodents (and in fact most mammals) form a complicated network of sensors called the vibrissae system. 

Around a rat’s muzzle is a particular arrangement of highly specialised hairs. These are notably thicker, longer and stiffer than the average hairs found on the rest of the rat’s coat, but the differences don’t just end there. 

The follicle for this hair is much more intricate than those of most other hairs. It is a swollen sinus of fluid surrounded by nerves and muscles. 

As unappealing as that may have sounded, it actually means that this long thick hair turns into a precision instrument designed to collect detailed information on its environment. 

The nerves surrounding that sinus are so sensitive that they are capable of picking up the size, shape and texture of objects as well as being able to sense changes in air pressure. 

In addition, these hairs can be moved back and forth, allowing the rat to interact with objects which are still some distance away from its nose. 

Moreover, the degree of fidelity for this mobile sensory web is assumed to be equivalent to that of our own fingertips. 

...if having a highly-sensitive schnoz isn’t super power enough, consider the rat’s whiskers.

Alex Wade, Wade Environmental

When a rat’s macro-vibrissae (big whiskers) encounter an unexpected object, they will stop and reorient their bodies towards this object for investigation.

Then a series of micro-vibrissae (smaller whiskers) will then dab against this object, helping to build up an ever more complicated mental image of the object in the rodent’s mind.

Think now to the last time you saw a rat encountering a new object or a trap; more often than not their body posture will be stretched out towards the object keeping their body back, their nose towards the object and their whiskers all reaching towards the new object.

Sounds like trouble

Finally, their sense of hearing. 

Rats are capable of both hearing and communicating in the ultrasonic wavelengths, as well as the more limited range of frequencies that humans can hear.

The reasons they do this are surprisingly clever.

There are two benefits to using ultrasound over other frequencies. Firstly, because most animals are primarily attuned to the more normalised bandwidth of frequencies, it gives rodents a ‘secure’ channel over which to communicate over short distances.

Rats are capable of both hearing and communicating in the ultrasonic wavelengths, as well as the more limited range of frequencies that humans can hear.

Alex Wade, Wade Environmental

The second reason has a little bit more to do with physics.

Ultrasound is made up of vibrations that occur at very high frequencies, unlike something like infrasound which is made up of vibrations at very low frequencies. 

Infrasound is how animals like elephants and whales communicate over great distances; the sound waves are so long and pliable that they can travel a long way, and more importantly they can easily bend and deflect around corners. 

Think of a car in an urban environment – you can hear the bass rumble while that car might be around a street corner and usually well before the other sounds 
associated with the engine. 

The reverse is true for ultrasonics, which are decidedly less adroit at ‘bending’ and usually get reflected straight back to the sender. This makes ultrasonics great for things like medical devices looking for kidney stones, and equally as great for rat pups wanting to get the attention of mum. 

Rat pups communicate within these frequencies precisely because ultrasound is so poor at travelling long distances. After all, if you are a small tasty morsel around the same dimensions as a jelly baby, the last thing you want to do is highlight your location to every predator out there looking for something to snack on.

These are just a few of the fascinating and unexpected ways that a rat experiences the world.

It is important to remember, compared to animals like us whose primary sensory cues are visual, that the world ‘looks’ very different to a rat. 

They sense the world with a preternatural acuity that we cannot even begin to fathom and the adaptations above are just the surface of our understanding.

We must always try to ‘think like a rat’, but this is certainly something much harder to do than to say.

Source: PPC109