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Sea Savvy - May 2007

Dealing with the things that scurry in the night

Dealing with the things that scurry in the night

How to keep the occasional mouse or roach from coming aboard, and what to do if they take up residence

We were sitting in the warm saloon of an old wooden powerboat one late-fall evening, listening to the wind howl as it kicked up an early snow flurry. Henry, who owned the old boat, had a bottle of wine, the contents of which were rapidly disappearing. Feeling rudely left out, I’m sure, a rat sauntered out from behind a timber at the end of the bookshelf opposite the dinette. It calmly walked to the middle of the shelf, turned, sat down, and stared at us. We didn’t need an introduction.

Henry had been talking about this rat for several weeks. He lived aboard with it and was much less enthusiastic about the relationship than was the rodent. Actually, Henry had been trying to get rid of his companion ever since the first night it pulled the covers off his feet while he was innocently sleeping. The screams echoed through the marina, and those sounds hadn’t come from the rat, who was really a quiet fellow. In his efforts to coax the rat either off the boat or into rat heaven, Henry tried all sorts of traps and tactics gained from local wisdom and marina lore. None had worked.

The uninvited appearance in the otherwise perfect evening caused an unexpectedly agitated state in the otherwise peaceful, laid-back Henry. Inspired by wine and emboldened by anger, he reached over and grabbed a rolling pin from the galley counter. The rat saw what Henry was about to do, but it didn’t flinch an inch. Henry flung the rolling pin at the rat with all his might. The rat could have reached out and caught the pin, avoiding a lot of trouble, but it elected not to. Instead, it ducked. The pin sailed past the rat, hit the rotten hull and continued, with almost no hesitation, on its flight and out into the cold night.

Henry had a new porthole in his hull. Actually, it was more like a new picture window. We left shortly thereafter. The snow swirling in through the hull had chilled the evening. The good news was that the rat also left. Apparently it didn’t like the icy air filtering down into the bilge. It was last seen, it’s reported, walking down the dock dragging Henry’s covers with him.

There are better ways to deal with rats on board, and better ways to deal with other unwanted visitors. This is such an important subject that I considered interviewing a panel of experts, but I couldn’t find anybody who would admit to being one. So I thought I’d say a few expert-like things myself. The first is that we do not have rats or mice or cockroaches, etc., aboard Chez Nous. We’re fanatics about this. But we have had an intruder or two in the past — whom we took care of immediately — and we have plenty of friends who’ve shared their experiences with us while drinking rum around a bonfire on the beach and who, under the circumstances, would admit to just about anything.

Attitude adjustment

But first things first. In order to maturely discuss this subject, we must get rid of the concept that if a rat comes on your boat it’s dirty. Well, the rat probably is dirty, but the boat isn’t … necessarily. Rats just have a habit of checking things out. And if your ordinary, average rat is walking down the dock on a Saturday night it might hop aboard even the cleanest boat. It also might be walking down the cleanest dock in one of the cleanest marinas on the coast. I’ve seen this. Of course, I’ve also seen lots of rats walking down some really dirty docks, especially near restaurants and fish-cleaning stations, and I firmly believe the law of averages is more on your side if you stay away from those. But you shouldn’t go on a guilt trip if your boat falls prey to pests.

In fact, a little-known fact about rats may startle you. They can climb aboard even when you’re safely out at anchor. This happened to some friends who were anchored in the Abacos. A Bahamian commercial fishing boat had dropped hook nearby, and a rat, apparently tired of seafood, jumped off, swam across the harbor, and climbed up their anchor line. Being thrifty people, they hadn’t been to a marina in months. Imagine their horror when they found unmistakable evidence of the rat and assumed they had been cohabiting for that long. Imagine their relief when someone came alongside in a dinghy and said, “If you just had a pit bull on board, he might have been able to stop that rat from coming up your anchor line.”

Not only should you not be ashamed if a rat comes aboard, you also may continue to hold your head high if cockroaches come aboard — as long as you declare war on them immediately. They love boats, even clean ones (clean boats, that is). And, as with the rats, you can get them on board even while anchored. Unbeknownst to many, some cockroach species can fly. If one happens to choose your boat to land on you’ve got troubles. If that one also happens to be pregnant, you’ve really got troubles. Although I’ve tried, I’ve never been able to determine the percentage of cockroaches that are flying around pregnant, but from what I’ve seen in a few dark corners, I think the number is large.

Does size count?

Size is important to this discussion in several respects, in addition to the size of the number of pregnant flying cockroaches. For example, many people seem to abhor large rats and think small mice are cute. Let me assure you that none of the above are cute when they walk across your face in the middle of the night, no matter how large or small. But we have found that small mice are slightly more preferable than large rats, because it’s usually easier to catch them in mouse traps than it is to catch large rats in rat traps. Some of the rats I’ve seen on the docks are big enough to hold down the spring with one foot, pick out the bait, then throw the trap down your hatch.

People also seem to think that the huge Southern/Caribbean-style cockroach — which is up to 1-3/4 inches long and is also known as the “American cockroach,” “La Cucaracha,” “cockaroach,” “Palmetto bug” or “747” — is more onerous than the cute, cuddly Northern style cockroach (German cockroach), which averages a modest 5/8 inch long. There is, however, some benefit that comes from the size of the large Caribbean style cockaroaches. Unlike your ordinary small cockroach or the rat that sneaks up the anchor chain, you can usually tell when a 747 cockaroach lands on your boat after a flight over the harbor. They are so big that you can hear the thump. And then you feel your boat heel as it scurries for cover. But this gives you a better chance of running out on deck and stomping on the thing before it goes into labor and begins a population explosion.

Understanding the threat

Rodents and cockroaches are somewhat challenged as to physical hygiene, and they all can get really hungry. If there isn’t enough food around — and sometimes even when there is — they eat things like electrical insulation off wires and rubber on hoses below the waterline. They can cause short circuits, fires and even sinkings in the right circumstances. They’ve also been known to bite people in the night, and they all can carry disease. The dead body parts and fecal pellets of cockroaches are considered to be household allergens just like those of dust mites, and these allergens are suspected of also triggering asthma attacks in some individuals.

Most of us are familiar with the problems from rats and mice, so let’s turn our attention to a few salient facts about cockroaches to demonstrate the seriousness of that problem. A scientific type of person once told me that there are around 3,500 known species of cockroach. I’m not sure how he knew, because he didn’t look old enough to have been counting that long. Perhaps the fact that there are so many species of cockroach explains the reason it’s hard to get much of a consensus on the subject except that they are all bad news. The following is a smorgasbord of varying cockroach observations.

Compton’s Encyclopedia reports that female cockroaches (it wasn’t clear to me which species) typically lay 16 to 45 eggs at a time, which take four to 12 weeks to hatch. The brownish egg cases of the Palmetto bug are purse-shaped, around 3/8 inch long, and are either laid loose or glued to walls or bulkheads in dark, moist places a few days after conception. After the immature cockroach (nymph) emerges from the egg case, it takes several months to mature and begin repeating the process. The nymphs grow by molting (shedding their hard exoskeleton). They remain white for a short while, then turn brown again.

At the HowStuffWorks Web site (, I learned that a female Palmetto bug and her young can produce about 800 offspring in the mother’s lifetime of about a year. The more prolific German cockroach and her young can produce up to 300,000 new cockroaches in her lifetime of also about a year. She carries her egg case (of usually around 40 “babies”) on her abdomen but drops them when they are ready to hatch. (I can’t say that I blame her.)

From an article at the University of Florida-IFAS Extension Web site (, I learned that the Palmetto bug can live two years, produce 20 to 80 egg cases in a lifetime, and that each egg case can produce 15 to 20 nymphs. This article also said that the German cockroach can live six months, carrying four to eight egg cases in its lifetime, with 28 nymphs per case.

One thing everyone seems to agree about is that the survival rate of the cockroach is notable; cockroach fossils date as far back as 320 million years. Those of us with really old boats won’t be comforted by the fact that a 300-million-year-old, 4-inch-long fossil was found in the Midwest. It also has been reported that they can go a month without eating and can live for a week or longer without a head. All of this implies to me that these guys are at least as dangerous as rodents — maybe more so — and I don’t want to coexist with any of them.

And there’s one other significant area of agreement. Whether the roach or rodent is big or small, and whether it’s on little sailboats or megayachts, cruise liners or tramp freighters, fishing boats or battle ships — they all like to go cruising.

Of course there are various other unwanted creatures that may populate your boat, including snakes, ants, weevils, wasps, spiders and endangered species. I hardly have space to discuss them all here, so I’ll discuss only rodents and cockroaches, since these are the more commonly encountered pests for most of us.

Avoiding them

Be very vigilant when bringing aboard groceries or packages, even newspapers and books. It isn’t unusual for a roach to be hanging out in a hand of bananas or down at the bottom of a paper bag. In the islands, we usually wash fruit in the sea before we bring it aboard (if it’s a clean harbor) or rinse it in chlorinated water. Roaches love glue. If you bring cardboard boxes aboard even for a short time, especially corrugated cardboard boxes, you might also be bringing roaches aboard.

Putting rat guards (like aluminum pie plates) on dock lines could help, but a determined rat or mouse can often find a way around them. Certain pets, such as aggressive cats and dogs, might help, but they’re not a guarantee. Closing off dorade vents and other points of entry also might help. Always keep a well-maintained, heavy-duty screen over vents. We tightly stuff towels into our anchor rode holes. Don’t create temptation by leaving edibles out, including pet food. It’s especially important to not leave edibles on deck. For example, many people will hang a hand of bananas or vegetables in the cockpit to mature. This is asking for trouble.

You can tell it by the pellet

The sooner you know an invader is on the boat, the better your chances of getting rid of it before it causes problems. Vigilance is key. Usually, one of the first signs that a rodent or cockroach is on board is activity from one end or the other. You’ll either notice that food has been nibbled or you’ll find droppings. Because of the latter, I long ago abandoned any attempt at using scientific-type names for these creatures. I call them all “stealth bombers.”

Unfortunately, if you’re not eternally vigilant, the droppings can sometimes be there long before you realize it, their creators multiplying and doing unseen damage. So it’s good to always be on the lookout for other clues. For example, a good clue that you’re hosting cockroaches is seeing several dozen head for the bilge when you turn on the light at night, but hopefully you’ll find out far before that.

Scurrying, muted rustling in the night behind liners, munching sounds in the night, and mysterious holes in food containers all call for immediate action, which begins with identifying the type of intruder. Big cockroaches can make noises so loud and leave droppings so large that the uninitiated may think they’re rats or mice. If you’re setting rat or mouse traps and the bait keeps getting nibbled with no rodents caught, think cockroaches.

Any little bites taken out of fruit, such as apples or oranges, should be fair warning.

You’d think that you could figure out who’s aboard because of indications on the food that’s being eaten. But the dainty nibbles of all three of these types of creatures can look very similar to most of us. If the rat is big enough you might see some tooth marks around the little hole in that Red Delicious apple, but not necessarily. If the cockroach is big enough you might see canine-like punctures, but not necessarily. Until you get this figured out, you can’t be sure whether to set out a mouse trap, rat trap or cockroach hotels. This is important because it’s no fun to get up in the morning and find that the cockroach hotels you set out the night before are all stacked up in a neat pile in a corner, covered with a mountain of rat droppings.

Sooner or later, in one context or another, you’ll see droppings. When you see those droppings on deck or in the galley, how do you know whether it’s a rat, mouse or cockroach? With a subject this important, you’d think you could find some authoritative discussion on it somewhere — at least in a West Advisor in the West Marine catalog. However, I haven’t found many people willing to discuss it.

Droppings often first show up in secretive places, like under the dinghy or under that nest of rags you left up on the bow for chafing gear when you anchor. Then they show up below deck in secretive places like under the galley sink. It’s not long before they show up below in not-so-secretive places, like beside the vase of flowers on the dining table or between the salt and pepper shakers that your dinner guest is reaching for. Here’s what you’ve perhaps wanted to know all your life about droppings. (Actually, it may be much more than you ever wanted to know.) These are general guidelines that may be helpful. We’ve collected them (the guidelines, not the droppings) from research that includes discussions over the years with those friends on the beach drinking rum around bonfires.

• The small cockroach generally leaves droppings that look like coffee grounds and are usually black.

• The large cockroach usually leaves droppings that look like cylinders and are usually black or dark brown. They can be up to 1/16 inch in diameter and about that long, possibly longer.

• Mouse droppings look a bit like thin grains of rice but are dark brown. They may be up to 1/4 inch long and will probably be pointy at the ends. (Trust me. All you have to do is to look very closely and you’ll see. If you don’t trust me, that’s OK.)

• Rat droppings look like mouse droppings but — you guessed it — they’re bigger. They may be lighter in color, too, and are usually a bit more rounded at the end than mouse droppings. They can be up to around 1/2 to 3/4 inch long. Fresh ones are full and moist, old ones dried and hard.

You’ll notice I used the word “usually” a lot. That’s because all sorts of unusual things can happen when you’re on a boat, especially with regard to rodents and cockaroaches. Like when you’ve been at anchor for a month and find droppings on your boat, but you know darn well that there’s been no 100-pound German shepherd aboard.

Getting rid of them

One friend solved his cockroach problem handily when he brought a few island geckos aboard his fine yacht. These friendly lizards were nice pets,

he believed. They would crawl out from under the cockpit cushions during cocktail hour, particularly when sat upon. They also liked hanging out in the head and would peep out, usually at guests, at some rather inopportune times. Our friend discovered that soon after the lizards’ arrival, the cockroach population noticeably decreased until it ceased to be a problem, as he defined it. When I visited him in another harbor a year later, the geckos were still there and had grown rather fat and happy. No, he wasn’t sure what they were eating at the time.

Another friend got a cat. He reasoned that the plan would work, since many Palmetto bugs are at least as big as mice. But the cat died. I’m not sure how the cat died, and, come to think of it, I don’t recall a funeral. But if your cat eats Palmetto bugs and lives, I am sure a lot of people would like to know about it. You might also consider breeding it.

We’ve read some very impressive cockroach-control advertisements, and the claims are heartening, with methods and devices even designed specifically for the big Southern brand of roach. The only problem is that these are designed for your typical household scenario. We all know that cockroaches love boats, because they love to hang out in warm, moist places, and boats are full of these. The advertisements speak glowingly of cockroaches carrying the poison back to the nest to share with their friends, thereby laying thousands of the creatures to rest. I’m not too sure this is exactly what I would want in my warm, moist places. I’m hoping that maybe they can come up with some chemical that will give cockroaches an insatiable urge to go swimming.

Nevertheless, it helps to always keep cockroach hotels (of which you will find various brands in your grocery store) or similar products strategically placed around the boat for preventive measures. Don’t wait until you think you have cockroaches. Most dark, moist places are good places for them. Don’t place them where a pet or child can get to them, and follow directions carefully and heed all warnings. These hotels must be renewed periodically.

Of course, you’re aware of the fumigation sprays or “bug bombs” available in grocery and other stores. These aren’t as effective on boats as they are in houses, because boats have so many small, hidden, tightly contained spaces. If you use them, open up everything you can and remove as much as you can from below. Protect children and pets from residue. Birds are particularly vulnerable to sprays. Heed all warnings and carefully follow directions of any pest control product. If you have your boat professionally fumigated, be sure that the “professional” is aware of the special issues presented by boats.

Any time you see a cockroach on board, do whatever you can to safely (meaning forget the shotgun) kill it, and throw its body away. Don’t despair and give up the ship, thinking that just because you’ve seen one there must be millions. Perhaps the one you see, especially if in the daytime, will have just gotten aboard and won’t have had time to lay eggs.


Obviously, poisoning is not the ticket here. You don’t want a rat or mouse to go down into its nest and die on your boat. Always carry an ample supply of both mouse and rat traps on board. The simple, old-fashioned, spring-loaded death traps (“snap traps”) are the best. You can store a lot of them without taking up much space. Carrying cage traps to save the cute little creatures isn’t my idea of good sense. If you want to operate a zoo, it’s best to do it ashore.

If you think you have a rodent on board, it’s important to start setting traps immediately. Set at least several groupings in the places you’ve seen evidence, as well as any other logical places. Rats usually like to run along walls rather than across open spaces, so many advise setting traps next to the hull sides or bulkheads, with the bait facing the vertical surface. Wherever you place the traps, be sure no one is going to get into them, including pets. They can be very painful if accidentally sprung, and they can break the bones of toes, fingers and other parts.

There are different theories as to bait. We’ve found that pieces of apple with a peanut butter topping work well, while bacon does not. If you find that the creature has consumed one type of food on board, consider using that. Be extremely careful when setting traps; it’s easy to catch yourself if you don’t handle the job correctly. When placing them, be careful to keep fingers and other parts away from the danger area in case the lock should slip. Be patient. Rats are reported to be more cautious than mice and may need several days to get used to traps before taking the bait. Mice are said to be more curious, so they might take the bait more quickly. If you’re not sure which you have, set both types of trap with varied baits.

When you catch the rodent, be very careful about handling it. Don’t touch it. They can carry serious disease, and sometimes they’ll still bite, even though you can’t imagine how they could possibly be alive. They can bite through thick gloves. If possible and legal, throw the rat or mouse and the trap overboard using a boat hook or some other means that keeps it away from you and others. I know this may offend some environmental concerns, but you as a species deserve some protection, too. I wouldn’t be surprised if in some jurisdictions it may be illegal to throw rats overboard. But consider for a moment who writes the laws.

I said earlier that I wouldn’t be able to cover all pests. But because of popular demand, I will suggest what to do to get rid of snakes. Very carefully and patiently observe the snake’s habits. Learn when it likes to sun itself in conspicuous places, and learn when it likes sleep in an out-of-the way hidden place. Then, during one of those latter times, sell the boat.

Tom Neale is technical editor for Soundings and lives aboard a Gulfstar 53 motorsailer. You can buy his book, “All in the Same Boat,” at .