This Simmering Heat – Pest Aug/Sept 2022

This last couple of weeks have seen some of the hottest temperatures in living memory for the UK.  Temperatures so barbarically hot that many of us haven’t encountered them short of a holiday somewhere only two junctions shy of the surface of the sun, or maybe just the equator.  Suffice to say the increase in heat has come with some of its own challenges, not just for us working in it, but for the pest animals simply just trying to survive it.

This simmering heat.

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This last couple of weeks have seen some of the hottest temperatures in living memory for the UK.  Temperatures so barbarically hot that many of us haven’t encountered them short of a holiday somewhere only two junctions shy of the surface of the sun, or maybe just the equator.  Suffice to say the increase in heat has come with some of its own challenges, not just for us working in it, but for the pest animals simply just trying to survive it.

The need for heat is a biological imperative.  Chemical reactions under normal circumstances require an abundance of two things, heat and a lot of random chance.  In nature this means that the chemistry we usually take for granted inside our bodies when replicated outside of a cell takes a long time, sometimes even measured on the scales of eons.  However, it is abundantly apparent that most biological entities do not have eons to wait for some of these simple chemical processes to unfold and to overcome this rather unseemly lack of patience all living organisms have developed a little bit of a work around, in the form of enzymes.

Enzymes are made from one or more proteins that in turn are made from amino acids, which I am also obligated to now inform you after long tradition are what we must refer to as the ‘building blocks of life’.  But enzymes although seemingly magic in their abilities, have a very specific range of conditions within which they can function.  If temperatures drop too low for example, they will slow down and not be able to work rapidly enough to facilitate normal biological functions, which is generally considered to be a ‘bad thing’.  Conversely as temperatures rise they will reach an optimal range within which they will function at peak efficacy, yet not far beyond that however these tiny powerhouses will start to break down and return to their original constituent parts ceasing to have any functional effect.  This breakdown is precisely the same effect you witness when you cook an egg and the albumen turns from a translucent goo to a thick white rubber.  The same process can occur within our own cells and when it happens within a still living animal it has similarly drastic effects.

Temperature therefore can be a tricky balance to master, with too little forcing enzymes to cool down and become less effective and too much will see enzymes heat up, denature and cease to function ever again.

Nature has had quite some time to work at this balance and has adapted to these constrictions in a number of ways, with some animals such as insects they rely on their environment to provide the necessary temperatures to bring their enzymes to peak efficacy whilst others such as rats and mice take responsibility for the regulation of their own body temperatures instead.  In the case of insects the relinquishing of the responsibility for generating a stable body temperature has proven to be a highly energy effective strategy, as it require little biological effort on behalf of the insect to function (other than to ensure that they position themselves in the right place for the right length of time).  These animals are known as poikilotherms and although it might seem like a tremendous risk to leave the efficacy of one’s own cells to the whim of the sometimes rather capricious weather systems there are some distinct advantages to it.  Firstly, poikilotherms don’t need nearly so much energy to survive, having let the environment and its ambient temperature do much of the heavy lifting for them, this makes them exceedingly efficient and reduces their need for food and resources significantly when compared to say a mammal of comparable size.

This temperature relationship can be seen with many pests insects such as bedbugs whose generational times have been extensively documented and clearly shown to decrease the higher ambient temperatures become.  This shift in behaviour and biology is not just anchored to bedbugs however, as these temperatures increases so does almost all pest insect activity, maturity and reproduction.  The changes in biological function, the slow downs at low temperatures and increases at higher temperatures have another key effect whereby it provides insects with a form of seasonal biological clock, letting them synchronise their own drivers and behaviour with those of their food and habitats, ensuring that they emerge from their eggs, pupation or diapauses at the correct times as well ensuring that investing effort into producing viable offspring will occur at times of the year which are most likely to support growing populations.

Individually insects are generally quite mobile, and therefore can situate themselves in locations which are most conducive to their development and survival, but what happens when we consider insects which all utilize the same space such as a nest?

Social insects struggle to move to lower temperatures when the ambient environment becomes challenging to their survival.  Some social insects such as ants have a limited degree of flexibility and are able to move their larva and even their nests to cooler environments, but insects such as bees and wasps are unable to achieve the same feat quite so readily.  Therefore they need to employ other mechanisms in order to compensate for otherwise lethally high temperatures.  To start, social insects will offset small rises in temperatures by using their own individual biomass to transfer heat away from their nests.  By warming up inside the nest then leaving to find cooler locations they act as tiny heat sinks moving heat away from the nest.  As temperatures rise higher flying insects such as bees and wasps will then employ additional mechanical controls such creating forced ventilation with their wings at the entrances of their nests to draw hot air out of their nests.

Finally some species of paper wasp will even use water deposited directly onto the fabric of their nests to create an a evaporative cooling which works on the same principle as many of the industrial units used around the world by humans.

All this goes to prove just how reliant insects are on living within a range of just the right temperatures, so much so in fact that some species of insect will use this intolerance to high heat as a defensive mechanism.  Certain species of bee will create ‘bee balls’ and mob marauding wasps and hornets which threaten their hives.  This mobbing will cause the inside of the bee ball to reach temperatures higher than that which the attacking insect can survive and in short order result in cooking them in situ.  We are witnessing here in nature precisely how the use of our own specialist heat treatment tools work, and why they are quite so effective.  Direct heat treatments such as those provided by the use of a steamer or the use of space heaters work with exactly the same lethal efficacy by taking the core temperature of insects beyond a level feasible for enzyme function and structure.

Animals such as mammals employ an entirely different strategy when it comes to temperature control.  These animals are known as homeotherms, and they maintain a consistent temperature through the constant metabolism of food.  This steady state of core temperature allows their enzymes work in a much narrower range of temperatures (meaning they can get away with fewer enzymes to do the same amount of work) but also means that they have a greater intolerance of change within that steady state, so the environment needs to be more strictly controlled.  Whilst this may seem like a lot of effort it simultaneously allows these animals to remain more active and functional even at low environmental temperatures.  This strategy allows for mammals to (on the most part) remain active all year around and to colonise environments which would usually be too cold for insects to be active, let alone prolific in.  As a result the adaptations we observe in mammals that assist in thermoregulation tend to largely be geared towards keeping heat in.  Rats and mice will nest in burrows or within bundles of highly insulative materials, they tend to grow thick coats of fur, will huddle together for warmth and will carry a small amount of fatty tissues which can be used both for insulation and as an energy reserve to ensure that a constant core temperature is maintained.  In fact if we were to look at the behaviour of mice as a case study we can see that most of their behaviour is in fact driven by a need to preserve temperature, after all they are a small object with a small volume and a large surface area which will struggle to hold onto its core temperature.

But what happens when we take an animal which has adapted over millions of years of evolution to retaining heat and suddenly place it into an environment where there are temperatures which are too high?

Rats and mice cannot reduce their temperature in the same way that other mammals such as humans might.  Humans have evolved the rather nifty trick of being able to sweat in great prefusion, whilst this might lead to awkward social encounters or embarrassing moments during public speaking events, this unsightly flop of sweat keeps us largely alive when temperatures start to soar.  Although rats and mice can and will sweat to an extent, the amount of exposed skin available to achieve this feat is greatly diminished by the presence of the aforementioned fur and therefore their ability to reduce their temperature is similarly compromised.  This means that alternative mechanisms need to be employed to try and reduce their temperatures.  Excessive grooming is once such adaptation, creating a false sweating effect, another is limiting behaviours to the coolest times of day (even more so in the case of the already nocturnal rodents) and finally they increase blood flow into their tails to encourage heat dissipation.

You can see therefore that an excess in heat is far more dangerous to all animals than a decrease, so with that in mind if all animals need to keep cool just as much as they need to keep warm how might we be able to use these behaviours to our advantage?

Water, the limiting resource.

All animals need water in order to achieve basic metabolic function, but additionally we see that it is a ubiquitous adaptation in almost all animals to achieve basic cooling through evaporation.  This means that as temperatures increase so does the need to find water.  We can use this shift in biological drivers to our advantage by using it as a tool to detect presence and movement of pests.  If we know that a rat not only needs water every day, but will need an increase during hotter periods then we can use these spikes in activity to look for the signs of pest infestations around areas known to be rich in available water.  The margins of puddles, water traps, or other similar reservoirs will become more heavily frequented, leaving tracks and signs that will be giving away even the most fledgling populations of rodents.  Additionally we can look at using tools which will play into this increased need for water, the use of bait formulations which have been moisture balanced or enriched will become progressively more favourable as the abundance and access to water becomes more limited.  Finally the use of water itself, either in the form of placements of fresh water to lure rodents into engaging with your pest management programs or the use of specially formulated liquid baits will play into the pests behavioural changes. A final note to consider in this sweltering weather is that it is not just pest animals whose behaviour will be effected by these changes.  Other small rodents will be similarly stimulated, and this in turn may well lead to increased interactions between non target animals and our areas of operation increasing the potential for environmental risks.

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