If you hate cat fleas the best place to live in America is Colorado

Someone asked the question whether fleas don’t exist at a certain elevation above sea level. It’s a good question because my reference book on veterinary treatments for cats states that all cats can be affected by the cat flea “except for those living at higher elevations, because fleas do not live above 5,000 feet”. There are lots of cities and towns in Colorado above 5,000 feet.

I checked that out and a couple of ‘experts’ said that it isn’t about the elevation above sea level which prevents the existence of cat fleas, it is the relative humidity (rh) in the air. As the air becomes drier it becomes more hostile to the cat flea and vice versa. I’m not sure what to believe because my reference book is a very good one.

Colorado, USA, a place where there are less cat fleas!
Colorado, USA, a place where there are less cat fleas! Photo Pexels on Pixabay.
Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

However, it is certainly true that temperature and humidity play a role in the survival and development of the cat flea. A study published as long ago as 1981 states that the upper and lower temperature limits for the development from egg to adult of cat fleas are 32 and 13°C. Also, in a relative humidity of 92% adult cat fleas are larger than those which have developed at 50% relative humidity.

Importantly, the study states that at a temperature of 27°C for a greater than 50% chance of survival of the mature eggs the relative humidity must be a minimum of 33%. For lava it is 50% and for pupa it is 2%. Cat fleas live longer in a higher relative humidity and decreasing temperature.

The study confirms that if you live in an area which is very humid you are more likely to have cat fleas troubling you and your cat.

The Northern Colorado Pest & Wildlife Control website tells us that fleas can live at higher elevations including in Colorado. Their advice is contrary to that provided by the four experienced veterinarians who wrote the reference book I have referred to. However, they agree that fleas are found in lower numbers in Colorado because of the lack of humidity in that state.

how to keep fleas away from the home
Horrible things which can affect cat behavior! The cat flea is the most prevalent parasite on the domestic cat.

And it is quite obvious to any researcher that a large part of Colorado is situated well above sea level. All but one city (in New Mexico) above 9,000 feet in the US are in the state of Colorado. And all but five cities and towns above 8,000 feet are in Colorado. Similar statistics apply to cities and towns above 7,000. They will enjoy relatively dry air. The conclusion is that if you hate fleas and live in a humid state you might consider relocating to Colorado!

P.S. I researched why the air is less humid at higher altitudes and did not come up with a nice answer, sadly. One reason is that the air contains less moisture because it is thinner and the air is cooler. But that is not a complete answer. It doesn’t really matter but what might matter to the cat owner is that although fleas have all but been eliminated at say 9,000 feet, the dry air at such high altitude dries out the human skin which is something that may displease many cat owners.

P.P.S. Colorado is neither in the top 10 most friendly cat states nor the least friendly. It is middle-ranking.

The study referred to is: Influence of Temperature and Humidity on Survival and Development of the Cat Flea, Ctenocephalides Felis (Siphonaptera: Pulicidae).


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