Fleas are a ubiquitous parasite that just about everyone who owns a pet knows at least something about. This article is about what they are, how to control them on your pets, in your home and in the yard, along with some discussion of erroneous information about their control that one runs into often on the internet.

There are many species of flea but only one really affects us and our pets, the cat flea. Dog fleas are nearly extinct thanks to the cat flea's superior reproductive and feeding strategies. Cat fleas infest all sorts of animals including just about all mammals (even us, but only if forced to) and even birds. About the only other flea one might likely encounter on their pets are rat fleas (rare, but the bad guy behind the Black Plague in Europe centuries ago) and bird fleas (aka ‘stick-tight fleas). The latter look like miniature cat fleas but act more like ticks, just sticking to the fur and not moving around at all. You might find these on your dog or cat if she has been raiding bird nests, or have had a bird in their mouth recently. The cat flea, Ctenocephalides felis, is a blood sucking parasite that has an amazing ability to adapt to cold, heat, drought, humidity, lack of food sources etc. that is almost awe-inspiring. This tenacious parasite has several life stages from egg, to larva, to pupa, to adult, with the first and third stages being the toughest ones for us to deal with (at least in terms of getting rid of them). The third life stage, the pupa, is nearly indestructible (at least to our toxins) and can survive for many months in just about any environment (except extreme cold and full sun). Yet at the slightest touch or sensation of a mammal's presence or heat, the adults can pop out of these pupae like popcorn and feed immediately.

cat flea photo Wikipedia

Once on a pet, the cat flea lives its life there, leaving the pet only if scratched off (or forcibly removed in some other way, such as bathed or combed off) or dead of old age. However eggs readily fall off into the environment and hatch when the time is right (usually very soon). A cat flea can lay up to 50 eggs or over 1000 eggs in her lifetime (several months). Multiply this by the number of fleas often found on pets and that's a LOT of eggs that fall into the carpet or in the yard. The eggs hatch into small larvae that are vulnerable to desiccation, heat, drought, light, toxins etc. This is one of the weak links in a flea life cycle, but not an easy one to find, unfortunately. Then the pupal stage, (sort of like the cocoon stage of a butterflies life) lasts a very variable length of time (3 days up to a year).

The flea eggs are white, egg-shaped objects smaller than the head of a pin, but visible to the naked eye. These are usually only seen in long-haired pets, or on pets with severe infestations. Put your dog or cat on a dark blanket and rub the coat back and forth. You can sometimes see the eggs come off- they can be popped under your fingernail with little effort. Flea larvae are very tiny caterpillar-like creatures and almost never seen, and flea pupae are rarely seen, either. The adult fleas are small, dark brown and move quickly through the pet's coat (or hop onto your socks if there are large numbers in the carpet and yard)- you can easily see them if you are wearing white socks. The other identifiable objects one can see in flea infestations is what is we call, euphemistically, flea dirt (dried feces basically of digested blood). This is a black, dirt-like debris often found on your pet, usually near the rump mostly and can be seen when your pet's fur is rubbed back and forth and standing on a white sheet.

Fleas on your pets can cause a long list of problems starting with simple blood loss (even fatal anemia) if present in high numbers, to a variety of blood parasites and bacteria they can carry, and even severe allergic skin disease. In fact the most common allergy seen in the pet cat and dog is the flea allergy (allergy to flea saliva)- far more common than any food allergy or even environmental allergy. The veterinary and pet industries make millions, if not billions, of dollars a year on trying to control fleas on your pet and in the yard. I think there must be more products made to kill fleas and prevent flea infestations than just about any other category of pet product (aside from pet food) in existence

Topical and Oral Flea Products

Back when I first got out of veterinary school, we were basically in the infancy of trying to control flea infestations on our pets and in our environments. There were dozens and dozens of shampoos, powders, sprays, spot-ons, and collars, all fairly toxic not only to the fleas but to us and our pets as well (though thankfully to a lesser degree). Unfortunately fleas had developed some degree of resistance to almost all of these toxins and battling fleas was a constant effort. We shampooed them, we combed them, we applied leave-on products and we treated our houses and yards with all sorts of poisons and products. The effect was, if enough effort was applied, a stand-off. Some products stood out as being more effective than others, though. Organophosphates, carbamates, and the many related poisons were the initial mainstays against fleas. All these products ended up being rather toxic to children and pets, and have, for the most part, been replaced today, though some are still on the market. Then the pyrethrins and pyrethroids (synthetic pyrethrins) became the main stays of control in most cases. About the only one of these ingredients in full use still today are the pyrethroids, synthetic versions of pyrethrins, a ‘natural' product derived from Chrysanthemums. All are fairly toxic to children and pets and should be used extremely carefully. Pyrethroids are relatively non-toxic to dogs, but very toxic to cats, so be sure you don't use these products on them. Unfortunately most of the cheap over-the-counter (OTC) products have pyrethroids in them and sometimes pet owners like to ignore the big warnings all over the packages that these are NOT cat products. But even small dogs frequently become toxic with these products, even sometimes if not overdosed. There are many other excellent and safer options today.

kitten

cats, and especially kittens, are hightly sensitive to nearly all the older OTC flea products.

cat safe product

This 'spot on' is one of over a dozen brands designed specifically for cats, and though it does contain a pyrethroid (Etofenprox), it is in much lower dose that what would normally be applied to a dog so it does have a much higher safety factor (but probably lower effectiveness as well) than the canine products have. This product also has an IGR (insect growth regulator- see below) which is a very safe product indeed, but does not kill fleas directly.

The first products that actually had a real effect on flea control during my years as a veterinarian were the insect growth regulators. These products did NOT kill fleas at all, but rendered them completely sterile. This may not sound like a great breakthrough, particularly in light of today's very effective flea-killing products, but it was huge progress back in the 1980s and actually really knocked out flea populations effectively and extremely safely. These products were the first truly safe products that worked. Many of today's products still have these in them (see chart below).

Then, about 15 years ago, a product that had been used in agriculture for years, and commonly found in the garden section of your local nursery, was reformulated for dogs and cats and actually had a nearly 100% effectiveness killing fleas fairly rapidly, and was incredibly safe for mammals (Imadcloprid). This product, and many of the newer spot-on products since, have seriously revolutionized the battle against fleas. No longer were we just at a stale mate, but now had something that was easy, safe and effective. The battle of course continues, but it is much easier to win nowadays. Now there are at least half a dozen safe, effective and simple products to use on fleas from spot-ons (topical preparations in very small tubes applied to the skin and either absorbed immediately or spread across the skin's surface) to oral medications (see chart below). It is interesting and ironic that the safest flea products available are the ones you need a prescription for from the veterinarian, while the much more dangerous ones are the ones sold over the counter (OTC) and can be purchased by anyone at any age. You would think it really should be the other way around.

advantage

This product was the first out that contained topical product that actually proved SAFE and EFFECTIVE killing fleas rapidly. Now there are over a half dozen equally effective and safe products on the market

These products are divided into two completely different categories as far as the FDA is concerned. One category include the pesticides. These are the products that primarily work on the surface of the pet or on the environment (area sprays, dessicants, shampoos, collars, some spot-ons, bombs, yard sprays etc.). These are not considered drugs and are not restricted by the FDA, but the EPA. These do not and never did need a doctor's prescription for use. The other products are the internally effective ones (oral and spot-ons). Since these are considered drugs, they need a prescription, and possibly always will. Many associate drugs with toxicity, and topicals with safety. However, in most cases, the topicals are the much more toxic products while the drugs being used today for flea control are far safer and much less toxic. This confusion and resulting fear and even paranoia has lead many pet owners to avoid these safer veterinary products and to rely more heavily on either the highly toxic inexpensive pesticides, or upon products that have no effectiveness at all (such as most, if not all, ‘natural' products). See chart below for summary of these products.

pesticide sentinel

the product on the left is a topical product that is considered a pesticide, even though it does get absorbed into the pet's system, so it is controlled by the EPA; The product on the right is a prescription drug for fleas (and heartworms, primarily) and is under FDA control. The first product is OTC at a pet store while the latter product can only be purchased through a veterinarian.

Fleas in the yard

This is a weak link in the circle of flea control on most pet animals that go outdoors. Indoor animals can often be treated 1-2 months with some of the better flea control products and that will be the end of the problem. However, outdoor pets are exposed to an endless potential source of fleas from roaming cats and other dogs that come into the yard, as well as wild animals that often carry and drop flea eggs (cats and opossums tend to be the largest contributors to the flea-egg load in most rural and suburban yards). Most home-owners efforts seem erroneously aimed at killing fleas in the lawn, where fleas are actually the LEAST likely to be found anywhere on the entire yard (including indoors). Fleas do NOT like sunlight and lawns are generally in full sun. So the last place one should put any effort into ridding fleas in the yard is the lawn. Fleas like shade and so do most pets for that matter. So where cats and dogs are sleeping or avoiding the sun, or wild animals are spending most of their time, is where one should concentrate their efforts at controlling the yard fleas. These are under shrubs, on the porch and alongside the house and the perimeter of the property.

squirrel dave

Some wildlife are among the weak links to keeping fleas out of the yard; lawns are the last place to look (and treat) for fleas.

Newer topical and oral products work so well in killing fleas that many times yard treatment is unnecessary, since the pet will act as a flea magnet and go about the yard killing the fleas by just having them jump on the pet. This will unfortunately involve some infestation time and owners will see fleas on their pets over and over again. This frustrating situation is the primary cause of most owners wrongly concluding that the current flea products being used on their pets are not working. This incorrect assumption is what leads most owners to trying out other less effective over-the-counter (OTC) products that are also often more toxic and dangerous. I have heard over and over again how this or that product sold to them by a veterinarian no longer is working on their pet and I know that it simply is not true. There is very little to no evidence (yet) of resistance to any of the newer, safer and more effective products (though that possibility is always a concern). The problems are with owners expectations- most expect an instant kill, which most products do not deliver. And most owners also expect to never see another flea on their pet again, which is simply unrealistic and cannot possibly happen if there is an endless source of fleas in their yards.

yard sprays yard spray 2

some products that can be used on the yard specifically for fleas. There is some degree of resistance in many flea populations to all these products, however, and most of the products will eliminate most other insect life as well

If one is overwhelmed with outdoor fleas, there are numerous products on the market for this problem. Unfortunately the emphasis and research on flea control over the last twenty years has been on products given directly to the pet. There are really few new environmental products, and most involve relatively toxic poisons from which many fleas have developed at least some resistance. Additionally all environmental flea products are fairly nonspecific in their spectrum and will easily kill beneficial insects and arachnids as well. Fortunately fleas tend to live on the ground, so product application should only be on the ground, not on bushes, trees and flowers where bees might be affected. As mentioned already, owners should concentrate their yard efforts on the shady areas nearest the house, or anywhere their pets sleep in the yard. Some efforts might also concentrated on the yard perimeter, as that is usually where cats and opossums walk along and drop flea eggs into the yard.

pussy on bench pussy on wall

resting spots in the shade are where most fleas end up in the yard; cats walking along perimeters tend to drop a lot of flea eggs there.

The following table is an incomplete list of the chemicals and products used to treat fleas on your pet and in the yard and includes relative effectiveness, safety (toxicity), frequency of application, prescription etc. Note: Hazard numbers are rough estimates only.

Chemical Name

Some Common Names

Class of toxin or General Category

Hazard to Pet (1- minimal, 10- dangerous)

Hazard to non-target species

Form/Use

Prescription or OTC

Imidacloprid

Advantage, Premise, Marathon

Nicatinoid

1

3

Topical/ yard

‘OTC'

Fipronil

Frontline, Termidor

GABA receptor blocker

1

4

Topical/ yard

‘OTC'

Selamectin

Revolution

Avermectin

1

2

Topical

Rx

Spinosad

Comfortis

Spynosin

1

2

Oral/ yard

Rx/ OTC

Nitenpyram

Capstar

Nicatinoid

1

2

Oral

Rx

Dinotefuran

Vectra

Nicatinoid

1

1

Topical

‘Rx' for now

Metaflumizone

Promeris

Semicarbazone

1

1

Topical

Rx

Lufeneron

Program

IGR

0

1

Oral

Rx for now

S-Methoprene

Precor, Frontline Plus

IGR

0

1

Topical

Rx

Boric Acid

Many

Inorganic compound

2

2

House

OTC

Diatomaceious Earth

many

Inorganic compound

2

2

House/yard

OTC

Dichlorvos

Vapona

Organophosphate

8

8

Topical/house

yard

OTC, but partially banned

Tyrichlorfon

Neguvon etc

Organophosphate

6

8

Topical/house

OTC

Chlopyrifos

Dursban

Organophosphate

6

8

Topical/yard

OTC

Phosmet

Phosmet

Organophosphate

6

8

Topical/yard

OTC

Diazinon

Knox-out

Organophosphate

6

8

Topical

House/yard

OTC

Malathion

Organophosphate

5

8

House/yard

OTC

Tetrachlorvin-

phos

Rabon

Organophosphate

7

8

Topical

OTC

Carbaryl

Sevin

Carbamate

5

5

Topical/yard

OTC

Propoxur

Baygon

Carbamate

5

5

yard

OTC

Pyrethrin

Pyrethrin

3

3

Topical/yard