You Can Tell It By the Pellet
By Tom Neale

When you see those droppings on deck or in the galley, how do you know whether it’s a rat, a mouse, or a cockroach? With a subject this important, you’d think you’d find some authoritative discussion on it somewhere, at least in one of the West Marine Advisories in their catalog.

I want to make it very clear from the beginning that we never see these droppings on OUR boat, but I’m just asking the rhetorical question in case you ever see them on your boat. Or maybe a friend of yours will admit to seeing them on his boat. So let’s talk about it that way. We can talk about your friend and my friend who need to figure out who the heck left those droppings.

Now you may think this isn’t serious or isn’t important, but it is. A cockroach can quickly become a million cockroaches. A rat isn’t quite that good at it (although I do hear that they have more fun at it) but one rat can become a big bunch of rats a lot faster than you’d think. And even though they may look like your children’s hamsters, the only “like” in the equation is that the rat will “like” to eat the hamster. A mouse maybe isn’t quite as bad as the other two except as to the RP factor (rodent proliferation). But all three of these creatures are somewhat challenged as to physical hygiene and they all can get really hungry. If there isn’t enough food around, and sometimes when there is, they eat things like electrical insulation off wires, rubber on hoses below the water line, or, best of all, the plastic in those really good smelling hoses that carry stuff from your head to wherever it goes.

Usually the droppings are the first clue you have that one of these things is aboard. They show up on deck in secretive places, like maybe under the dinghy or under the nest of rags that you left up on the bow for chafing gear when you anchor. Then they show up below decks in secretive places like maybe under the galley sink. It’s not long before they show up below deck in other secretive places like right beside the vase of flowers on the dinner table or right between the salt shakers that your dinner guest is reaching for.

You’d think that you could figure out who’s aboard because of the food that’s being eaten. But the dainty nibbles of all three of these types of creatures can look very similar. 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 punctures in what’s left of that leg of lamb you’d saved for a special occasion, but not necessarily (usually there’ll be nothing left to see at all.) Until you get this figured out, you can’t be sure whether to set out a mouse trap, rat trap, or some cockroach hotels.

Dropping a Hint 1. The small cockroach generally leaves droppings that look like coffee grounds. Usually they are black. (Unless it really is coffee grounds that you forgot to clean up after breakfast and you drink that funky foo foo designer coffee.) 2. The large cockroach usually leaves droppings that look like cylinders. They can be up to 1/16 inch in diameter and about that long. They are black or dark brown. Click Here for More Tips

My friends (who travel on their boat a lot in southern latitudes) usually go nuts and set out all three. But this can lead to additional problems. Some of the rats that hang out around docks are so big that if they spring a mouse trap while going for the bait, they pry it open and set it again right where you’re going to step out of your bunk next morning. Some of the Caribbean cockroaches are so bad that when they want the bait in a rat trap, they’ll eat the rat trap first, saving the bait for last. And then there are those really fine times when you get up in the morning and find all the cockroach hotels stacked up in a neat pile in a corner and covered with a mountain of unidentifiable droppings.

Some think they can tackle this problem of creature identification by figuring out where the creature came from. For example, they think that if whatever it is that’s aboard came aboard very recently and they’ve been out at anchor for the last month, it can’t be a rat or mouse. The unenlightened might also think that it couldn’t be a cockroach, but the unenlightened don’t know that cockroaches can fly. As horrible as it is, you just have to get used to this fact when you’re cruising in the lower latitudes. The only thing you can do about flying Caribbean cockroaches is to hope that when they land on your boat, they make a soft landing. I’m told that crashing cockroaches have been known to sink boats. The unfortunate fact is that any of this trio can come aboard whether you’re at a dock or not. But this fact, as you will see, has shed some light on the situation, albeit in a somewhat perverse manner.

I had a friend once who got a rat aboard while anchored out in Abaco. The rat left a commercial fishing smack anchored nearby (assumedly he got tired of the smell), swam across the anchorage, and climbed up my friend’s anchor line. They soon knew that something was aboard and searched high and low. After a whole day of searching, they literally took everything out from below and piled it on deck and then put it back, hoping to find a nest. Nothing. They then began to hear it at night walking around on deck. From the sounds of the foot falls they figured it was a rat. They figured it was a pretty big one because the boat would heel from side to side as it walked around the deck. They huddled below during the tropical nights terrified, with every crook and cranny sealed. After one of those harrowing nights my friend was in the head and just happened to look up into the dorade vent. There he saw a huge mound of fur nestled down on the broad mesh screen that was across the vent portal. He ran screaming for his fishing spear and, as everybody else in the anchorage watched over coffee in the cockpit, he bent over and wildly speared through the deck opening of the dorade vent until finally he was successful and withdrew the spear with one large rat impaled. Now, think about. If you were a rat getting speared to death as you were cowering over a broad mesh screen which was, in turn, over a head, what would you do? Needless to say, the floor of the head compartment was covered with rat droppings after the foray.

In case you’re wondering what the point is, this friend’s experience provided a basis for making a determination of pellet identification. It’s the way scientists do it. Once you find a known standard you can rule out or rule in other things, or something like that. Over rum on the beach that night, we all compared notes and, in the interest of the brotherhood of cruising, I thought you’d like to know the conclusions. So now you’ll have a basis for determining who’s aboard when you see droppings on your deck. A rat, a mouse, or a cockroach. For the scoop on dropping identification, see Tom’s Tips.

Copyright 2004-2009 Tom Neale