Why do pests exist and how can we protect ourselves?

Contents

• Wild vs. urban: why do these species adapt so well?

• Biological balance or health risk: the advantages and disadvantages of cohabitation

• Natural methods vs. professional intervention: selection criteria and recommendations

• Conclusion

A cockroach crossing your kitchen at 2 a.m., scratching noises in the partitions, a colony of ants settling on the worktop: we've all experienced it at least once. And the first question that comes to mind is often, «Why do these bugs exist? As if nature had made a casting error.

Things to remember

• We approach the existence of pests from the angle of evolutionary success and biological adaptation to human environments.

• By citing scientific mechanisms of proliferation, we transform a nuisance into an explainable phenomenon, while providing objective criteria for choosing the right time and method of professional intervention.

• Why do these species adapt so well?

• The pros and cons of living with pests

Spoiler: she didn't miss a thing. Pests aren't a bug in the living world. They are species that have won the evolutionary lottery, organisms so well adapted that they thrive where others disappear. The problem is that their favorite playground is often ours. Our homes, our cellars, our attics, our entire cities.

Understanding why pests exist is the first step to knowing how to react. Not in a panic, not with old-fashioned recipes that work one time out of ten, but with informed decisions. That's exactly what we're going to do here: break down the biology behind pest proliferation, weigh up the real risks, and give you concrete criteria for choosing between personal action and professional intervention.

Wild vs. urban: why do these species adapt so well?

700 generations. This is what the brown rat (Rattus norvegicus) has accumulated since it began colonizing European cities in the 18th century. 700 generations of learning, natural selection and genetic refinement in an urban ecosystem we've built ourselves to be comfortable. Stable temperature, abundant food, shelter everywhere: what we've optimized for ourselves, we've optimized for them too.

The adaptability of these species is astounding. Take the German cockroach. A study published in Scientific Reports in 2019 by researchers at Purdue University has shown that certain populations develop cross-resistance to several classes of insecticide in just five generations. Five. In a species whose reproductive cycle lasts just a few weeks, that means that in less than a year, your supermarket insecticide can become totally ineffective.

Why do we have pests in the first place? Because we give them exactly what they need. A rat needs 25 grams of food a day. A poorly-sealed garbage can, leftovers in an open composter, cat croquettes left outside: it's a feast. French cities produce an average of 1.2 kg of waste per inhabitant per day. Do the math for Paris and its 2.1 million inhabitants. We're talking about thousands of tons of food resources accessible every day.

The urban ecosystem has another peculiarity: it lacks natural predators. In the wild, rodent populations are regulated by birds of prey, foxes and mustelids. In the city, these regulators are virtually absent. The domestic cat, often cited as a solution, does not compensate. A study by Royal Society (2020) has shown that domestic cats mainly kill easy prey (birds, small lizards) and avoid adult rats, which are too big and aggressive for them.

Insects are the same mechanism taken to extremes. A wasp queen can create a colony of 5,000 individuals in a single season. Bedbugs, thought to have been eradicated in the 1950s thanks to DDT, have made a spectacular comeback since the 2000s. Their secret? A combination of resistance to pyrethroids and increased international travel. These are highly effective pests.

There's one point we often forget: these species don't «choose» to invade us. They follow resource gradients. Heat, water, food. When these three elements converge (and in our homes, this is systematic), pest proliferation becomes a matter of time, not chance. The real question is not «why do they come», but «what is it about me that still attracts them?.

Biological balance or health risk: the advantages and disadvantages of cohabitation

Which is the most harmful animal? The question is often asked, and it's a tricky one. Because «harmful» is not a biological category. It's a label we attach to species based on the damage they cause us. In France, the regulatory framework speaks of ESOD (Espèces Susceptibles d'Occasionner des Dégâts), a more precise term than the old «nuisible», which suggested that certain species were intrinsically bad.

Let's be honest: some of these species play a role in biodiversity. Wasps pollinate. Rats help decompose organic waste in sewage systems. Even spiders, which many people hate, regulate mosquito and fly populations. Completely eliminating a species from an ecosystem, even an urban one, can have cascading effects beyond our control.

This doesn't mean we should accept to live with just anything. The health risks are real, documented and sometimes serious. The brown rat is a vector of leptospirosis, a bacterial disease that causes around 600 cases a year in France according to Santé Publique France, with a mortality rate of 5 to 20% for severe forms. Cockroaches are associated with the aggravation of asthma in children: a study by the National Institute of Environmental Health Sciences showed that cockroach allergens were present in 85% of urban dwellings tested in the United States.

Damage-causing species are not limited to health risks. Rodents cause around 25% of unexplained electrical fires by gnawing through cable sheaths. Termites can compromise the very structure of a building. We're talking thousands of euros worth of damage, and sometimes buildings rendered uninhabitable.

So, where do we place the cursor? The answer depends on the species, the context and the level of infestation. A spider in the corner of a ceiling, leave it alone. An Asian hornet's nest two meters from a terrace where children are playing, we intervene immediately. Between the two, there's a whole grey area where public hygiene and common sense must guide the decision.

What's certain is that ignoring the problem is never the right strategy. Pest populations don't stabilize on their own in an environment as favorable as our homes. They grow exponentially until a resource becomes limiting. And when that resource is space, they spill over into the neighbor's yard. Pest control is not a whim: it's a necessity for public health and the preservation of the built environment.

Natural methods vs. professional intervention: selection criteria and recommendations

Three mice in a garage is not the same thing as rat tracks in an entire condominium. The answer can't be the same either. And that's where a lot of people go wrong: they apply a DIY solution to a problem that requires expertise, or conversely, they call in a professional for a situation they could have handled on their own.

Natural« treatment solutions have their place. Peppermint essential oils effectively repel certain rodents in the short term. Mechanical traps (swatters, nests) work for limited populations. Diatomaceous earth is an effective natural insecticide against crawlers. But, and it's a big »but«, these methods have clear limits.

Here's how to assess the situation:

• Level 1: Spot observation. You've seen an isolated individual, with no recurring tracks (droppings, grease marks on baseboards, visible damage). You can try an independent approach: sealing off access points, eliminating food sources, setting a few traps. Give yourself two weeks to evaluate.

• Level 2: recurring signs. You regularly find signs of pests, traps are often triggered, and the problem persists despite your actions. It's time to consult a professional for a diagnosis.

• Level 3: Established infestation. Frequent noise, property damage, odors, sightings of several individuals in broad daylight (for rodents, this is a major alarm signal: it means that the population is so dense that some are being driven from their usual hiding places). In such cases, you need a professional pest control service, without hesitation.

Why does the professional make the difference in serious cases? There are three reasons. First, he identifies the exact species. An anti-mouse treatment won't work on a cockroach, and a product against German cockroaches may be useless on Oriental cockroaches. Identification determines the whole protocol. Secondly, he has access to professional biocides whose efficacy is incommensurable with consumer products. Finally, it treats the cause, not just the symptoms. Plugging a 2 cm diameter entry point in a pipe is often more effective than ten traps.

An important point about insect control specifically: for bed bugs, professional intervention is not an option - it's the only realistic solution. The failure rate for «in-house» treatments exceeds 90% according to field feedback from certified companies. These insects hide in gaps of just a few millimeters, lay eggs resistant to common insecticides, and can survive for over a year without feeding. With no need for heat treatment or targeted chemical protocols, you just move them from room to room.

Cost often holds people back. For a private individual, a standard pest control operation costs between 150 and 300 euros. Bedbug pest control, on the other hand, costs between 400 and 1,000 euros, depending on the surface area. It's an investment, yes. But compare it to the cost of an infestation that takes hold: replacement of gnawed cables, treatment of an entire building rather than a single apartment, even health problems. Pest control, when carried out at the right time, always costs less than inaction.

A final word of advice: when choosing a service provider, check that they are biocide-registered, and ask for a written intervention plan. A serious professional doesn't just «apply poison». He'll explain what he's doing, why he's doing it, and what follow-up he's planning.

Conclusion

Pests don't exist to annoy us. They are extraordinarily well-adapted species that exploit the resources we unwittingly make available to them. Understanding this mechanism means regaining control of the situation.

The key is to act at the right time with the right method. Prevention first: eliminate access, food and water sources. Surveillance second: be alert to the first signs. Finally, intervene quickly, as soon as the situation goes beyond what you can manage on your own.

If you have any doubts about the level of infestation in your home, don't let the situation get any worse. Contact a certified professional for a diagnosis. Better a call «for nothing» than a colony that's been living in your partitions for six months.

Frequently asked questions