American Fancy Rat & Mouse Association

This article is from the Summer II 1998 AFRMA Rat & Mouse Tales news-magazine.


By Nichole Royer, Edited by Carmen Jane Booth, D.V.M.

Whether you call them bugs, creepy crawlies, or ectoparasites, none of us like to think of parasitic critters living on our pets. In fact, these unwanted miniature livestock that love to take up residence in our favorite rodent’s fur can be the bane of a rat or mouse fanciers existence.

It is very fortunate that most rodents who are raised and kept under normal household conditions never encounter problems of this type. It is important though for all rodent fanciers to be familiar with the signs of infestation, and the various methods of treatment, simply because ectoparasites can have a detrimental effect on the health of our pets, and in some cases their human companions as well.


Dog and cat fleas are small brown wingless insects. These insects spend much of their life living away from your pets (in the carpet, upholstery, your pets bedding, etc.). They crawl on to your pets (and you) to feed on their blood.

In order for rodents to have dog and cat fleas, they must be brought into the area in which they are living from another source. Usually household dogs or cats are to blame, and by the time the fleas are found on the rodents the household is rather heavily infested. It is fairly uncommon to find fleas on rats or mice.

Because fleas are relatively large (about 2 mm) they are easily seen, particularly on light colored animals. They are large, dark, oblong objects that will race through your pet’s fur at an astoundingly quick pace.

On dark colored animals fleas can be difficult to spot. A simple test is to hold your rat or mouse upside down over a white tissue and brush its hair backwards. If specks of dark colored “dirt” fall on the tissue, place a drop of water on them. Flea droppings consist of digested blood, so if the tissue turns red, your pet probably has fleas.

Fleas will often cause your rat or mouse to scratch some, and they may develop some hair loss or possibly scabs around the neck behind the ears. Because fleas suck blood, severe infestation can lead to anemia. Fleas also can transmit other parasites, most notable of which is tapeworm.

True rodent fleas are a lighter amber color. These usually are not seen, since they require contact with wild rodents. Domestic dogs and cats, as well as humans, rabbits, and domestic rodents can all be bitten by these parasites. Due to the fact that these are the hosts that can potentially carry and spread the plague, it is very important to prevent contact between wild rodents and domestic pets (or ourselves).


Like fleas, lice are cigar shaped thin wingless insects that suck their host’s blood. Unlike fleas however, lice are species specific. You can’t get rat or mouse lice, and neither can your dog (and your rat can’t get human lice either).

Rat lice spend most of their lives on their host animal, laying their nits (eggs) on the rat or mouse’s hair. They are smaller than fleas, usually ½–1½ mm long, and are tan to light brown in color.

Because they are smaller, lice are more difficult to spot than fleas. They are most commonly found above the tail and behind the ears. The simplest way to find them is to gently lift the hair on the rat’s backside and look at the rat or mouse’s skin. If you see what looks like a piece of dirt, hold still and watch it. If it is a louse, it will get up and walk away.

Often, rats and mice that have lice will have fur that looks ruffled, and feels thin. Rats may or may not have scabs around their neck and behind their ears.

Lice are usually transmitted through animal to animal contact, but they can also crawl off the critter and be transmitted in food, bedding, or on your hands and clothes.


Though extremely rare, I have heard of two cases of rats having a tick attach to them. I suppose it would be possible for mice to get them as well. Ticks are related to spiders and live by crawling onto an animal, sinking its mouth parts through the animal’s skin and engorges on its blood. When engorged they appear to be large round flat objects that are attached to the animal on one end.

Ticks prefer to live in areas that have dense brush, so unless you allow your rodent pets to play in such areas, they are unlikely to pick them up. It is also possible for your dog or cat to bring a tick into the house, or for you to bring one in on your clothing, but in both these cases the dog, cat, or yourself are more likely to end up with the tick than your rat or mouse would.

Tropical Rat Mites

The tropical rat mite is similar to a tick, only smaller (about 1 mm when engorged). It’s about the same size as a louse, only round instead of cigar shaped. Fortunately they are not very common, at least not on rats I have come into contact with.

Tropical Rat Mites typically live in small crevices, and only crawl onto the rat to feed. They can be brought in through direct contact with other rats, as well as on you and in bedding. Humans may also be bitten by this critter.


There are a several other kinds of mites that rats and mice may get. All are microscopic and cannot be seen by simply examining the animal. They usually live on the skin or in hair follicles, and taking a skin scraping and examining it under the microscope is one of the only ways to identify them. Unfortunately, more often than not the scraping does not have any mites in it, so you get a false reading.

These creatures are also relatives of spiders and ticks, and they live by sucking the blood of their victim. Mites appear to cause much more intense itching than most of the other parasites do. In rats, the first signs of a problem is thinning of the hair around the neck and shoulders. This is quickly followed by the appearance of scabs. In severe cases the animal may lose hair all down the sides of their body, and may have open weeping sores.

Mites are not usually as apparent on mice. Often a mouse will simply have a ruffled coat, and look a little off. On closer inspection you may find the mouse has scaly skin, or if its fur is dark you may see what looks like dust that doesn’t come off when you blow the hair open.

Fortunately, mites spend their lives on their host animal, and most do not bite humans or other animals. Some mite species can and do infect humans as well as our domestic pets, including rats. The scabies mite is one that is the most problematic. Mites are usually passed along through direct contact from animal to animal. Often they will exist on a rat or mouse for some time without causing any problems, symptoms only appearing when the animal gets stressed through illness or old age.

Eliminating Parasites

The first step in eliminating parasites is to figure out where they came from in the first place. Until you do, you will not be able to stop them from coming back.

Often a new rat or mouse brought into the colony can bring with it some unwanted passengers. It’s a good idea to closely examine any new animals for problems, and if in doubt, treat them. Another frequent source of problems is the occasional wild rodent that comes in for a visit.

Bedding is another source of problems, particularly if it is exposed to wild rodents. Buy bedding and food in unopened packages that have not been exposed to other rodents. If you allow your rats outside, be careful that they do not go where wild rodents are likely to have been.

Another frequent carrier of parasites that can effect our rats and mice are domestic fowl. Chickens are frequent culprits, and it is a good idea to handle your rats and mice first, then tend to the birds.


Always before treating your pets, talk to your veterinarian about parasite problems and the proper treatment program. It is best for a veterinarian to diagnose, prescribe, and treat diseases.

There are a number of products on the market that work very well to eliminate parasites in rats and mice. The most popular right now is Ivermectin. Ivermectin is actually a livestock medication used to eliminate many kinds of parasites, both external and internal.

There are several ways to give Ivermectin to rats and mice. The most effective seems to be a solution of Ivermectin in propylene glycol. This is available through your veterinarian. (One or two drops are placed on the neck between and behind the ears and rubbed into the fur, the animal’s cage is cleaned, and this is repeated 14 days later.) Many veterinarians will choose to give Ivermectin in its injectable form.

Some people give a grain of rice size dose of Zimmectrin, a horse wormer that contains Ivermectin, to rats. I do not recommend this, however, as I have had several people tell me that their rats have ended up having convulsions. Never try this method with mice—those people who have used even a minute dose have had serious complications.

Though Ivermectin is the most effective treatment we have found, there are others as well. Products made for treating kittens have proven to be reasonably effective, but not necessarily safe, on rats and mice. Often a bath in a diluted solution of kitten flea shampoo will help control most parasites. Kitten flea powder can also be used, both on the adult animals, and in the bedding. Don’t use products made for dogs.

Remember, for those parasites that are likely to crawl off your rat or mouse, you must also treat their environment. A thorough cage cleaning and litter change, at the same time as treatment is always a must for any type of parasite. For fleas, lice, and tropical rat mites, it’s a good idea to treat your house as well as using commercially available insecticides. Just remember, always carefully follow the directions for these products, and don’t use them on or near your critter’s cage.


Rat Health Care, 4th Edition by Debbie Ducommun
The Merck Veterinary Manual *

Bug check

Here is a simple way to check for external parasites on your rats and mice

  1. Hold your rat or mouse in your hand facing you. Does the hair lie flat or look ruffled or fluffy? If it does, you may have a problem.
  2. Feel your rat or mouse’s fur. Does it feel rough, thin, or dirty? If so, you might have a problem.
  3. Turn your rat or mouse to face away from you. Run your finger against the fur, or blow on the coat so that you can see then skin. Look for dark pieces of dirt (particularly the kind that move). Also look for dust or debris that sticks to the fur and doesn’t blow or rub off. These are good signs that your critter may have fleas or lice.
  4. Part the fur around your rat or mouse’s neck, cheeks, and under the chin. Do you see any scabs? Do you feel any? If so, and if you don’t see any dark moving critters on your rat or mouse, you probably have mites.

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Updated April 5, 2014