Ask the expert: Entomologist Matt Green answers common questions about pests

Rentokil research entomologist Matt Green answers common questions about pest risks, prevention, and treatment, and separates a few enduring myths from scientific fact.

Q: When does an insect become a pest?

“There is no universal number. Whether an insect constitutes a pest problem depends on the species, the setting, and the potential consequences. A single cockroach in an operating theatre, for example, is a serious hazard, even if the likelihood of one reaching that environment is low.

“The same principle applies to flies. A single fly at a waste site is expected and may not warrant action. In a hospital ward, operating theatre, or food processing area, however, fast intervention is essential because it could transfer bacteria from contaminated surfaces to clean ones.

“Ultimately, the threshold depends on what matters most in a given environment. A pest may threaten health, damage a building, contaminate food, or cause enough disruption to affect someone’s daily life.”

Q: Are the same pests a problem everywhere?

“No. Geography, climate, buildings, and human activity all influence which pests people come across. For example, the five most common pests in Minnesota may be very different from those in New England,” Matt says.

“Termites and mosquitoes are particularly relevant in parts of the southern United States, including the Gulf States, while timber buildings may be susceptible to carpenter ants and carpenter bees. Further north, where it’s cooler, rodent activity may be more of a problem.

“Human activity is another major driver of pest movement. International trade and travel can transport insects beyond their established ranges, including species that might otherwise spread slowly. Cockroaches can be transported in goods and belongings, while bed bugs often hitchhike with people from place to place.

“So pest risks depend on both the local environment and the movement of people and materials. Pest tolerance can also vary between communities, and attitudes towards control are influenced by culture as well as biology.”

Q: Is it worth waiting to see if an infestation goes away?

“Waiting can allow an infestation to grow, making it harder and potentially more expensive to control. It’s always easier to deal with pests in the early stages of an infestation,” Matt says.

“Some destructive pests, like termites, can cause damage before people realise they are there. With bed bugs, delays can allow the population to spread and increase the discomfort and distress experienced by occupants.”

Q: Can DIY pest-control products solve the problem?

“DIY products can temporarily remove the pests you can see, but they may not stop them from returning because they do not necessarily reach the source of the problem,” Matt says.

“The effectiveness of any treatment depends on identifying the correct species. Killing visible insects is all very well, but you also need to think about what attracts them and remove food sources and hiding places, or block entry points; otherwise, they’ll only come back. Worse, DIY heat treatments introduce serious risks; online advice like using propane burners for bed bugs is extremely dangerous.” 

Q: Why do treatments sometimes appear not to work?

“Resistance isn’t simply about one tough insect surviving; it develops across a pest population. When a treatment kills only susceptible pests, it creates selection pressure, where resistant individuals survive, reproduce, and pass those traits to the next generation, especially in fast-breeding species. 

“That is why professional pest management involves more than repeatedly applying the same chemical. Where resistance is suspected, technicians must switch to products with a different mode of action or use non-chemical alternatives like heat treatments for bed bugs, where resistance simply cannot develop.” 

Q: What is the biggest cause of pest outbreaks in commercial premises?

“Poor hygiene is the simple answer. Access to food and waste can support flies, ants, and cockroaches, making them harder to control. Regular cleaning is therefore an important part of prevention, particularly in food service and other environments where food is stored, prepared, or consumed.

“But hygiene is not the only factor. Pests can exploit gaps around doors, damaged screens, and other weaknesses in a building’s exterior, so proofing measures are equally important, such as repairing doors, sealing gaps, or fitting fly screens.

Q: What should hotels do about bed bugs?

“Training staff to notice the signs is the biggest thing. Hotels can’t completely prevent guests from bringing in bed bugs, but trained employees can help detect them before a small population grows into a larger infestation. The earlier you handle a bed bug population, the more likely treatment will succeed,” Matt says.

“Housekeepers are particularly well placed to notice warning signs, including spotting and cast skins. Thoroughly cleaning after a successful treatment is also advisable because removing old evidence makes subsequent activity easier to recognise.” 

Q: Are cockroaches as indestructible as people think?

“No. Cockroaches are resilient, but their supposed invincibility owes more to popular culture than biology. They’re not difficult to kill when the right methods are used.

“The claim that cockroaches would survive a nuclear explosion is also misleading. Although cockroaches can tolerate more radiation than humans, they would not necessarily survive the heat, blast, or extreme radiation produced by a nuclear explosion.

“Their speed and unusual movement may contribute to their formidable reputation. Cockroaches walk on six legs, jog on four, and run on two,” Matt says. “They gradually stand up more as they run faster.

“Cockroaches can also survive for an unexpectedly long time without their heads. Under laboratory conditions, this can be up to around 30 days. Outside the laboratory, infection and environmental pressures would be likely to kill them sooner.”

Q: How long can bed bugs survive without feeding?

Bed bugs can survive for extended periods under controlled laboratory conditions, but the idea that they can wait indefinitely is exaggerated. Bed bugs raised for generations in laboratory culture may live for a year, but those found in the field today need to feed probably every 45 to 60 days,” Matt explains.

“Conditions inside an occupied building differ from those in a laboratory, and survival times can vary. Simply leaving a room unused for a short period should not be assumed to resolve an infestation. Bed bugs hide effectively, and professional assessment is advisable where activity is suspected.”

Q: What is the difference between venomous and poisonous?

“Venom is actively delivered through a bite, sting, or other specialised mechanism, often to capture prey or as a defense. Poison causes harm when it is eaten, touched, or absorbed. In simple terms, a venomous animal delivers the toxin to you, whereas you come into contact with or consume a poisonous animal.

“Bright colours and stripes can sometimes warn that an animal has chemical defenses that could be harmful.”

Q: Will climate change affect urban pests?

“Pests already established in the local environment are among those most likely to respond to changing conditions—things like mosquitoes, termites, and rats,” Matt says.

“Warmer conditions could encourage some species to spread gradually into new areas. Higher temperatures may also affect the speed of insect development. Stored-product insects, for example, could complete their life cycles more quickly, resulting in more breeding cycles within a season and potentially increasing damage to food.”

Q: What is the most important first step after finding a pest?

“Do not assume that every insect requires the same response. Record where it was found, look for other signs of activity, and get help to identify the species.

“The appropriate action depends on the species, the extent of the activity, and the setting. A pest inside a manufacturing facility may require a different response from the same species found outdoors. Similarly, an insect that is harmless in one location could indicate a hygiene, health, or structural risk elsewhere.

“The real test of a good pest controller is their ability to explain what the customer needs to do to prevent a reinfestation. That may mean improving hygiene, removing food and shelter sources, sealing potential entry points, or changing how pest activity is monitored and reported."