Sugar and Spice and all things Mice (and Rats)

Winter is a time of year which usually sees rodents coming in from the wilderness and pushing at the peripheries of the areas we are looking to protect.

But what is it the drives their behaviour?  It is all too easy to just pass rodents off as mindless vermin, automaton which do nothing more complicated than react to stimulus in a predictable way.  But anyone who has spent more than a passing moment watching rats and mice knows that this could not be further from the truth.

We are going to start 2022 with a look into what it is that makes rodents tick, and how you might be able to use that information to increase the efficacy of your programs.

How to build a rodent in four simple steps (and how to make their strengths our advantages).

1. Teeth.
   To start, we should really look at the feature which gives rodents their name.  The shape and distribution of their teeth.  The most striking feature is of course the large orange incisors at the front of the mouth.  They are formed from a layer of super hard enamel resting on a bed of softer dentin.  This layering effect means that the sharp hard edge of the enamel is supported by the more elastic dentin behind creating a cutting tool which is self-repairing as well as self-sharpening.  Not only that but these materials and design have created teeth capable of chewing through all but the most stalwart of building and storage materials.  Moreover these teeth are continually growing, meaning that given sufficient time and inclination there is almost nothing that a rodent could not one day chew its way into.  This propensity to chew on almost everything in their environment is the reason that rodents are named as they are, with the Latin for rodere quite literally meaning ‘to gnaw’.  Of course, chewing a lot of inedible and indigestible material presents somewhat of a challenge for a rodent’s digestive tract and as such there is another feature of rodent dentition which compensates for this insatiable desire to gnaw.  The diastema is the large gap between the incisors and the molars where you would expect to find the second incisors, canines and premolars in other mammals.  This gap provides a buffer zone in which rodents can evaluate whether what they have just eaten if in fact worth the effort of swallowing and subsequently digesting.  If a material is deemed unworthy of consumption it is simply spit out and discarded, great news for the rat as it saves the trouble and biological costs involved with attempting to digest wood pulp or masonry, terrible news for a pest manager whos choice in bait was so wildly unpalatable the rat deemed it to be more effort than not to continue to consume it.
   This behaviour of continual gnawing and selective consumption can be used to our advantage in several key ways.  Firstly, gnaw marks are an excellent indictor of rodent activity.  The size, frequency and abundance of gnaw marks can be used to establish species, infestation age and size.  Secondly it teaches us that rodents are discerning in their choice in food, and that top quality components in your formulation are as important (if not more so in some cases) than your choice in active material.

• A superb sense of touch.
  The fur of rodents is unlike anything we as humans possess or can imagine.  Our own fur is largely for decoration and identification, for a rodent it forms a complex web of sensory inputs as well as providing much needed protection from the elements.  If you have ever taken the time to really look at the muzzle and the coat of a rat you will notice some incredibly unique traits.  To begin with, the fur on their coat is not all of a uniform length.  The topcoat is made from three distinct types of hair collectively called guard hairs, these hairs come in three lengths and not only provide environmental protection to the softer insulative undercoat but also provide a high degree of tactile sensitivity.  Additionally, the hairs which make the whisker of a rat are not a random scattering of protuberances, but a highly ordered and complicated arrangement of stiff hairs collectively known as the vibrissae system.  While both of these tactile senses feed back into the rodents’ exceptional sense of touch, it is this vibrissae system of rodents that can provide such a tantalizing sensitivity that rodents can easily determine the slightest changes in the texture of surfaces as well as sudden changes in air pressure.  This preternatural sense has led to rodents exhibiting a behavioural response known as thigmotaxis, which literally means “the motion or orientation of an organism in response to a touch stimulus”.  In the case of rodents, thigmotaxis will present in the tell-tale behaviours of running alongside wall floor junctions, not only does it afford safety, but also it allows the rodent an opportunity to generate information about their environment too.
  This thigmotaxis can be used to our advantage by initially being able to predict the movement of rodents in a known area of operation, allowing the placement of baits, boxes and traps in the most effective configurations and location.  Laterally this propensity to keep contact with solid objects makes rodents especially susceptible to treatment strategies that utilise gels and foams designed to be picked up on the coats of passing rodents and subsequently groomed clean.
• A supernatural sense of smell.
  A keen sense of smell is so important to rats and mice that they have evolved not one, but two biological mechanisms to provide to unique senses of ‘smell’.  The first is much like our own, provided by coiled epithelial cells in the nasal cavity over which air is drawn over and scents extracted through the keen perceptions of chemoreceptors embedded in this lining.  But that is where the similarity stops, as rodents then take this process to a level well beyond our own.  The chemoreceptors embedded on the surface of this coil are hardwired to special barrel structures contained within nodes within a very specific part of the rodent’s brain.  This means that to rodents’ smells will generate precise and predictable reactions within the brain, creating a ‘fingerprint’ for individual smells.  This specificity in olfactory awareness means that a rodent will have a very good idea of what it is they are approaching well before they have come close to it.  If this otherworldly olfactory augmentation wasn’t enough, the second sense of smell is even more remarkable and is provided by a specialist organ called the vomeronasal.  Unlike a conventional sense of smell described above, this organ (which humans have a non-functional, vestigial version of) is capable of sensing specific proteins and pheromones, specifically the proteins and pheromones found in the saliva, urine and feaces of other rodents.
  Whilst having a superhuman ability to smell urine may not seem like a massive advantage in life, rodent urine is exceptional in that contained within it there are special barrel shaped proteins, covered in receptors and then stuffed with pheromones.  The combination of protein, receptor and pheromone provides a secret code pertaining to such rodent orientated juicy tid bits as, “what age I am” ” How I am Feeling” ”Who I am, and how closely I might be related” and “Whether I’m up for a little nookie behind the grain silo”.  All of this information and considerably more is found in the excreta of rodents making it a messaging board hidden in plain sight, so it is less twitter and more… squeaker?.
  Although it may not seem how we can turn this to our advantage, we can certainly use this information to make sure we do not let them use this phenomenal sense to their own advantage either.  As we move around sites we will be shedding scent everywhere we go and on everything we touch, especially if we are not wearing gloves.  Additionally bait placements and hardware fresh from the manufactures floor will be a riot of bizarre smells.  When you consider that the sense of smell may well be the most singularly important diagnostic tool for a rodent, it then behoves us to make sure that what we leave behind is either as innocuous as possible, or as alluring to rodents as we can possibly make it.
• Advanced hearing.
  In part to compensate for their bad eyesight rats have a phenomenal sense of hearing which they have utilised to their advantage in a number of ways.  To start their hearing is so acute that it can in fact pick up noises well into the ultrasonic, and the reasons for this may be twofold.  The first of these is for communication, but maybe not in the way you imagine.  Rodent pups are born small, hairless and very vulnerable, in fact almost every predator out there would happily snaffle them up like so many delicious jellybeans the moment mum leaves the nest.  Therefore, it is of utmost importance that if the pups need to call out for mum, they do so in a way that doesn’t instantly flag up their position to every potential predator in the area.  To do this rodent pups will call out in ultrasonic squeaks.  Ultrasound is a fantastic tool for this purpose because not only will it be outside the normal hearing range of most animals, but it also travels very poorly.  Whilst at first glance the latter of the two might not seem like a benefit, but when you consider the pups are trying to call mum, if she is close enough to do something proactive she will return, but if she is not then you don’t want that cry for help peeling around the environment alerting all the other animals which can hear it to your location.  The other benefit from a rodents’ adaptation to ultrasound, is that it is believed that rodents do possess a rudimentary ability to echolocate.  This sense is no where hear as advanced as that of their cousins the bat, but it is sufficiently advanced that rodents being observed in total darkness (such as sewers) trying to traverse over vertical ledges are seen to hang their heads over the edge and ‘wobble’.  Rodents will repeat the motion until they come to a part of the ledge where the distance between edge and floor is manageable, giving rise to the assumption that rodents are using sound to gauge distance.
  Using this to our advantage teaches us the art of patience.  Its is almost a certainty that when you arrive on site, all the rodents there will be aware of you.  Marching from pillar to post, moving things and generally making a ruckus will ensure that all rodent all across the site will remain firmly ensconced in their hiding spots unless decidedly brazen.  If you have the opportunity observe the site calmly or set cameras that can observe discretely then do so and see what you can learn.

In closing the greatest tool we have at our disposal is to ‘know our foe’.  We can take these observations and extract from them the tactics required to implement ever more successful strategies.  Even the apparently unimportant nuances of behaviour we all so often dismiss as academic or trivial can all be repurposed, repackaged and restructured to increase the efficacy of all of our treatments.