Outsmarting Rodents: Behavioural Insights for Smarter Baiting and Effective Control
Understanding pest behaviour—especially when it comes to rodents—is essential for pest control professionals aiming to achieve swift and long-lasting results.
One key rationale that often arises when rodent control measures fall short is behavioural resistance. Unlike genetic resistance, which refers to the inherited ability to survive exposure to certain rodenticides; behavioural resistance—better described as behavioural avoidance, or bait avoidance—involves learning to steer clear of bait or bait stations, not because they’re ineffective, but because the rodents have learnt to recognise them as a threat.
We spoke to Envu’s Biologist, Dr Stefan Endepols, who has spent his career studying rodent behaviour, and works in R&D at Envu’s laboratories in Germany. Here he shares his valuable insights into the impact of behavioural avoidance and the strategies that can help pest control officers (PCOs) combat the issue.
He says, “Behavioural avoidance, simply means that rodents don't take up the bait, or that they are avoiding the bait station itself as of course most bait is now applied in this way.”
Rodents are highly intelligent and adaptive. Their ability to change feeding habits, avoid unfamiliar objects, and respond to subtle environmental cues and others in the colony, means that even the most potent control products can fail without a strategic, behaviour-informed approach.
“For example, we observed mice at a chicken farm that were only used to eating powdered chicken feed, and were only accustomed to eating very small particles. This made baiting with any solid kind of bait, like pellets or blocks, totally ineffective. We found that it was the texture and the physical appearance of the bait that caused the avoidance, not its smell and taste. When the bait was ground into smaller particles, we found the mice would then feed on it.”
“Bait stations are a good example of learned avoidance,” Stefan highlights. “Most bait stations are small, black plastic boxes. They are foreign objects in the rodents’ environment; they look strange, feel strange, and smell strange, which is why they are often avoided.”
“Regulations now mean that in most cases bait stations must be used. However, where it is permitted to place bait in a burrow or in a covered hole in the wall—like a more natural bait station—uptake can often be more effective.”
“It can also help to store bait stations in the place where they may be used, so that they can take up the smell of the environment and then do not appear as something new when they’re loaded with bait. We had a farmer store his empty bait boxes in his pig barn, so that when they were needed, the boxes were something that was common there; something rodents were used to.”
“Pest controllers with experience will make sure they know the site first, and learn how the rodents behave there,” he says.
“The initial inspection will determine where the rats and mice live, by following visible traces, like droppings. By developing a clear picture of real life conditions, bait can be placed where the rodents are most active, meaning they will only have a short distance to find it. Then they are more prone to accept the bait, rather than if they have to run a longer distance or find something new.”
Stefan describes how food availability can impact baiting success. “If feed in the environment is restricted then the alpha animals, as the most powerful, will feed first; with others in the colony having to join the queue behind them. But in environments with plenty of food available, often the alpha and the strongest animals will defend the food source, meaning the smaller rodents are more likely to visit a bait point first.”
This is when a rodent eats a bait, becomes ill, and then avoids that bait in the future. The rodent is able to associate the illness with the food source, and will then refuse to eat it, often for weeks.
Choosing high quality, attractive bait with excellent palatability, like those in our rodenticide range, can help overcome the issue of bait shyness, by helping to ensure bait is highly effective from the first time it’s used. Stefan explains:
“High quality bait formulation is very important. And high quality means an attractive taste and smell, as well as good nutritional value.
“It’s important to note that rodents can distinguish highly nutritious food from that of low nutritional value, and will opt for the most nutritious option. Therefore, artificial baits, or baits of low quality, will often be rejected and fail. But, if there's a nice smell, and a food source of value, they will choose to eat it.
Stefan continues. “In our bait development we only use very high quality foodstuff ingredients, that are often of human food quality; like rolled oats, high quality sugars and vegetable fats. We screen ingredients, in the lab and in the field, so we only use the ones rats and mice will choose to eat. We know what is the best, and most universally accepted.
“When there are situations when a particular infestation won't even take a high quality bait, this is where having a wide portfolio comes in,” Stefan concludes. “With our wide range of rodenticides, PCOs can choose another active ingredient or bait composition from the Envu range (depending from country) to change the approach, knowing all our options offer the highest quality formulations for the best chance of success.”
We spoke to Envu’s Biologist, Dr Stefan Endepols, who has spent his career studying rodent behaviour, and works in R&D at Envu’s laboratories in Germany. Here he shares his valuable insights into the impact of behavioural avoidance and the strategies that can help pest control officers (PCOs) combat the issue.
He says, “Behavioural avoidance, simply means that rodents don't take up the bait, or that they are avoiding the bait station itself as of course most bait is now applied in this way.”
Rodents are highly intelligent and adaptive. Their ability to change feeding habits, avoid unfamiliar objects, and respond to subtle environmental cues and others in the colony, means that even the most potent control products can fail without a strategic, behaviour-informed approach.
How behavioural avoidance impacts rodent control
What are the key features of behavioural avoidance, and what factors can influence this behaviour in rodents?
Neophobia
“Neophobia is when rodents are not keen to take anything different from what they are used to eating. This could be because of a different taste, texture or aroma,” Stefan explains.
“For example, we observed mice at a chicken farm that were only used to eating powdered chicken feed, and were only accustomed to eating very small particles. This made baiting with any solid kind of bait, like pellets or blocks, totally ineffective. We found that it was the texture and the physical appearance of the bait that caused the avoidance, not its smell and taste. When the bait was ground into smaller particles, we found the mice would then feed on it.”
Learned avoidance
Learned avoidance can manifest as avoiding bait stations or certain areas after negative experiences, as rodents associate bait, boxes or traps with danger and actively avoid them. Learned avoidance can also result in control methods becoming far less effective over time, requiring PCOs to adapt strategies and rotate bait types, or the application method, to stay ahead of this behaviour.
“Bait stations are a good example of learned avoidance,” Stefan highlights. “Most bait stations are small, black plastic boxes. They are foreign objects in the rodents’ environment; they look strange, feel strange, and smell strange, which is why they are often avoided.”
“Regulations now mean that in most cases bait stations must be used. However, where it is permitted to place bait in a burrow or in a covered hole in the wall—like a more natural bait station—uptake can often be more effective.”
“It can also help to store bait stations in the place where they may be used, so that they can take up the smell of the environment and then do not appear as something new when they’re loaded with bait. We had a farmer store his empty bait boxes in his pig barn, so that when they were needed, the boxes were something that was common there; something rodents were used to.”
Social learning
Rodents are social animals and will quickly learn what to avoid from others in the colony, so planning baiting strategies that reflect how the colonies have been living is key to success, as Stefan explains.
“Pest controllers with experience will make sure they know the site first, and learn how the rodents behave there,” he says.
“The initial inspection will determine where the rats and mice live, by following visible traces, like droppings. By developing a clear picture of real life conditions, bait can be placed where the rodents are most active, meaning they will only have a short distance to find it. Then they are more prone to accept the bait, rather than if they have to run a longer distance or find something new.”
Competing food sources
Rodents choosing to feed on other food sources over bait can be a problem, which is why one of the guiding principles of an Integrated Pest Management (IPM) approach is to take away as many food sources as possible, before starting any control regime.
Stefan describes how food availability can impact baiting success. “If feed in the environment is restricted then the alpha animals, as the most powerful, will feed first; with others in the colony having to join the queue behind them. But in environments with plenty of food available, often the alpha and the strongest animals will defend the food source, meaning the smaller rodents are more likely to visit a bait point first.”
Bait shyness
This is when a rodent eats a bait, becomes ill, and then avoids that bait in the future. The rodent is able to associate the illness with the food source, and will then refuse to eat it, often for weeks.
Choosing high quality, attractive bait with excellent palatability, like those in our rodenticide range, can help overcome the issue of bait shyness, by helping to ensure bait is highly effective from the first time it’s used. Stefan explains:
“High quality bait formulation is very important. And high quality means an attractive taste and smell, as well as good nutritional value.
“It’s important to note that rodents can distinguish highly nutritious food from that of low nutritional value, and will opt for the most nutritious option. Therefore, artificial baits, or baits of low quality, will often be rejected and fail. But, if there's a nice smell, and a food source of value, they will choose to eat it.
Stefan continues. “In our bait development we only use very high quality foodstuff ingredients, that are often of human food quality; like rolled oats, high quality sugars and vegetable fats. We screen ingredients, in the lab and in the field, so we only use the ones rats and mice will choose to eat. We know what is the best, and most universally accepted.
“When there are situations when a particular infestation won't even take a high quality bait, this is where having a wide portfolio comes in,” Stefan concludes. “With our wide range of rodenticides, PCOs can choose another active ingredient or bait composition from the Envu range (depending from country) to change the approach, knowing all our options offer the highest quality formulations for the best chance of success.”
