How Do Ships Deal With Unwanted Pests? 



According to the old saying, rats flee a sinking ship — but where do they go in the middle of the ocean? Seagoing vessels have dealt with unwanted pests since the earliest humans took to the water. How have methods improved to make this task more effective and less demanding? 

Controlling insect and animal infestations matters on everything from cruise ships, where crews must protect passenger health, to the tankers that carry bananas from tropical shores to your grocery stores. How do ships deal with unwanted pests? Here’s a comprehensive look. 

How Do Ships Deal With Unwanted Pests?

Common Pests Found on Ships 

The ocean is a mysterious place, one of Earth’s last uncharted territories. However, it might not surprise you to learn that the most common pests found on ships are the same ones giving humans grief on land.

Insects and rodents that contaminate food and spread disease create similar problems at sea. Sailors may encounter any of the following:

  • Flies and maggots
  • Cockroaches
  • Bedbugs
  • Termites 
  • Mosquitos
  • Mice
  • Rats 

How Do Pests Get on Ships? 

Although rats are prolific swimmers for their size, they tucker out after a few miles, and there aren’t many anthills in the middle of the ocean or garbage piles for flies to lay eggs. This reality begs the question — how do pests get on ships in the first place? 

The answer is the same way that humans do — they climb aboard. Some of them may enter by stowing away in hygroscopic cargo such as coffee beans, grains, nuts, or tea leaves. Others might hitch a ride from the pier.

For example, termites can infect a ship docked at an infested facility. Mice and rats can climb aboard via ropes or by hiding in cargo, and cockroaches and bedbugs may hitchhike via traveler’s luggage, just like they do on land. 

What Are the Risks of These Pests? 

Each pest type carries inherent risks to people, hence why they are considered menaces crews must eradicate.

Cockroaches are the most common pests among ships, with over 4,000 known species. They passively transport microbes that sicken people, including the virus that causes COVID-19. Bedbugs carry diseases and create painful bites, disrupting sleep. 

Mosquitos carry diseases like Zika, malaria, and yellow fever. Termites can threaten a ship’s structural integrity. Rats and mice massively spread disease and may bite passengers, transmitting rabies and other infections.

Ship Pest Control and Protecting Ocean Waters 

Controlling unwanted pests on ships might sound like a minor issue, but it is a matter of international security. Countries don’t want contaminated imports arriving on their shores that carry invasive species, which can take a devastating toll on their agricultural harvests and natural environments. 

Furthermore, governments have a responsibility to safeguard their citizens. Allowing unwanted pests to contaminate other vessels increases the problem’s spread. Contaminated shipments also add to pesticide use, which creates a separate set of potential health and environmental risks. 

Pests that threaten a vessel’s structural integrity can cause it to sink, risking human life and increasing ocean pollution. Finally, ships that carry passengers must protect their crews and those who pay for passage. Few travelers relish returning from their journey with a fresh crop of bedbugs in their luggage, necessitating the need to fumigate their homes. 

Prevention Methods for Unwanted Pests 

Vessels deal with unwanted pests through a combination of prevention and control. Preventative measures do what the name implies — they aim to keep pests off ships in the first place. 

Identifying the Risks 

The first step in ship prevention methods for unwanted pests is identifying the risks. For example, cargo labeled as high risk requires additional scrutiny. Pre-boarding inspections can identify contaminated packages before they get on board. Crews can insist on these for cargo from tropical countries where insect infestation predominates, cargo packed in materials that invite nesting, like cardboard and textiles, or cargo from areas with little regulatory oversight to prevent negligent omissions from untrained personnel. 

Crews may need to exercise good judgment when mandating additional inspection needs. For example, cargo loaded from docks that also permit liveaboard marinas may not trigger an alert for tropical locations or packing material. However, the risk of insect pests increases, thanks to all the nearby human life and associated activity that draws critters. 

Ships that carry human passengers also have unique risks. Fleas and bedbugs can spread as rapidly as at hotels. However, there’s nowhere for them to go but elsewhere on board, increasing the infestation risk, and disease spreads more quickly in close quarters. 

Crews should receive additional training in sanitation procedures, using best practices like washing linens in high heat to kill pests and monitoring for signs of infestation. They should report any suspected problems immediately, as delaying treatment allows the problem to spread. 

Deterring Pests from Ships 

Ships can also deter pests from entering. For example, performing regular inspections and maintenance to identify and fix holes and other entry routes keeps insect and rodent populations low. So does eliminating easy food and water sources, such as piles of open garbage and leaks. Routine cleaning discourages pests and quickly alerts crews to potential problems to take action before infestation occurs.

Ship owners should avoid letting vessels sit for too long and perform thorough inspections when such conditions occur. Pests can also damage wires and engine components that can cause big trouble at sea.

Finally, natural deterrent methods can help, such as:

  • Peppermint essential oil 
  • Cayenne pepper 
  • Dryer sheets
  • Irish spring soap
  • Ultrasonic devices
  • Mothballs
  • Cats
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Pest Control Methods on Ships 

Although prevention plays a crucial role in helping ships deal with unwanted pests, it’s often insufficient on its own. Furthermore, international rules may require certain crews to employ specific pest control methods. 

These practices aim to eliminate existing pests. As they often entail toxins or high heat, crews must take care to avoid contaminating humans and the foods they consume or damaging delicate electronic equipment. 


Fumigation is the most common pest control method aboard ships. Generally, crews hire professional exterminators to handle this process, although some large organizations may keep such individuals on their payrolls. 

Heat and Cold 

Some exterminators use thermal radiation to kill insect pests. Similarly, extreme cold temperatures can control certain life forms, keeping cargo safer. The problem with these methods is that crews must balance their effectiveness against the potential for damage to equipment and the risk to humans. 

Regulatory Framework and Guidelines 

One of the issues crews face when dealing with unwanted pests on ships is the various legal guidelines they must follow. These rules come down from multiple sources:

  • International maritime law 
  • The jurisdiction where the cargo departs
  • The jurisdiction receiving the cargo 
  • Individual trade associations and regulatory bodies 

The International Maritime Organization is a specialized UN agency that governs all aspects of shipping regulations. It includes ship design and construction and its operation and disposal. The International Maritime Fumigation Organisation Code regulates the safe use of pesticides on oceangoing vessels. 

Additionally, individual trade associations and regulatory bodies issue guidelines. For example, the Grain and Feed Trade Association (GAFTA) has over 1,900 members in 100 countries. It requires fumigators under its umbrella to maintain pest control standards and preserve the quality of traded goods. 

Finally, each port of call has specific guidelines for pest management when docking and departing their shores. Most large organizations devote an entire department to maintaining these standards and ensuring compliance. 

Procedures Around Infested Ships

Under International Maritime Law, a state is under no obligation to open ports to foreign ships. However, they must treat all ships equally. Additionally, they must follow certain rules when conditions of medical distress create unique situations.

Ports reserve the right to deny entries to ships they deem infested with pests if they meet three conditions: 

  • The restrictions must not be more severe than reasonably acceptable alternatives. 
  • Ports must rely on scientific studies to justify their denial.
  • Ports must convey their objections to the World Health Organization.

The difficulty of denying entry doesn’t eliminate problems. Many people remember the dramatic scenarios that played out during the height of the COVID-19 pandemic with passengers trapped on cruise ships. Such conditions can cause uncomfortable and unnecessary delays for crews and passengers alike — it’s best to prevent possible denials before they occur. 

Case Studies and Best Practices 

One crucial fact is that dealing with unwanted pests on ships is an ongoing process. Crews don’t have the luxury of implementing measures once and forgetting about them. As insects and rodents can climb aboard anytime, continual monitoring is key to a safe, pleasant sailing experience. 

For example, several cruise lines have faced scrutiny over bedbug infestations. As a result, Carnival has dedicated a team of personnel to monitor and eliminate pest issues. If they identify pest issues, they fully inspect passengers’ laundry and luggage, launder these items free of charge, and change all linens. They use special vacuums with escape-proof bags to eliminate intruders. 

Interior design also plays a role in deterring pests. For example, beds and dressers with lots of nooks and crannies provide ample living space for tiny insects. Clean lines and metal framing prevent fewer places for stowaways to hide.

Dealing With Unwanted Pests on Ships 

Mice, rats, and cockroaches don’t live in the ocean, but they can cause considerable trouble to seagoing vessels all the same. You now know how ships deal with unwanted pests. Use your knowledge to enhance your future travel experiences and develop greater compassion for crews who go to extraordinary lengths to ensure you have the products you need and love each day. 

Frequently Asked Questions

What Happens If an Infestation Occurs While a Ship Is at Sea? 

The treatment protocol varies for infestations that occur at sea. If the ship carries passengers, the crew may follow a procedure similar to Carnival’s for problems limited in scope to one or two individuals.

However, more widespread issues could result in court filings and monetary damages, although filing a maritime lawsuit is a complex process that requires filers to have considerable financial resources. Still, a class action could occur. 

In general, damages for infestations remain at the discretion of the individual cruise line. Therefore, you should call the carrier directly to discuss their policies before departure if you have concerns. 

What Chemicals Do Ships Use to Control Unwanted Pests?

Fungicides, herbicides, and insecticides can enter ocean waters, affecting wildlife. Therefore, those in the industry should adhere to regulatory guidelines to avoid accidental damage to oceanic ecosystems. 

Most insecticides work on the critter’s nervous system. Frequently used pesticides on ships include organophosphate, organosulfur, carbamates, formamidines, nicotinoids, pyrazoles, spinosyns, fumigants, and inorganic pesticides.

Can Ports Deny Entry to Infested Ships?

Ports can deny entry to ships, but there are rules around doing so. Restrictions of infested ships cannot be more severe than reasonably acceptable alternatives, and the port must present its reason for doing so based on scientifically backed evidence to the World Health Organization.

Can Passengers Request a Refund If Their Vacation or Shipment Was Affected by Infestation? 

The short answer is yes. The realistic answer is that it’s up to the individual company what financial remuneration they provide. Lawsuits take time and money, and those against foreign corporations are unlikely to lead to the desired outcomes. It’s best to research a brand’s reputation before you buy.

Do Passengers Face Penalties If They Accidentally Bring Pests Aboard? 

Only in very rare cases — such as a passenger attempting to board with a manifesto and a briefcase of live bed bugs. However, it’s nearly impossible to pinpoint the source of an accidental infestation. Cruise lines run a higher risk of lawsuits from affected passengers and should establish protocols, such as the ones Carnival implemented, to mitigate risks.

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