Fleas transmit Bubonic Plague, you avoid Yosemite National Park. It’s a bit of a one sided relationship.
Fleas are a parasitic species that pierce the skin of warm blooded hosts, and use blood as a requirement to reproduce for their life cycle. They are flightless, amazing jumpers, and you are not likely to see them due to their minute size (<4mm long). Fleas are also exceptionally hardy and are not crushed easily. The biggest sign of this pest is the telltale itch and bite. Much like a mosquito bite, flea bites generally have one bite made in the center. The reaction from the body is also similar with a raised irritated bump at the site of the bite.
Many flea species can live for up to 3 months, and one female depending on the species can produce upwards of 5000 eggs in her lifetime. There is a reason that fleas produce an aversion in almost every media representation. Historically fleas are hard to treat for because of how their populations can explosively grow/spread in a home, in a neighborhood, and in a city. The best basis for this aversion besides the general annoyance of having fleas is that of disease. Fleas of rodents species such as the oriental rat can carry the bacterium yersinia pestis, aka the Plague.
Many children are taught about the European Black Death in primary school; otherwise known as the Bubonic Plague. Of a span of less than 10 years in the 14th century, upwards of 200 million people died in a European outbreak of the disease. This estimate does not include other outbreaks around the same time both in China and the Middle East, which were both in the millions as well. 200 million people. That number is around the entire population of the United States in 1960’s alone, and only about 100 million less than the country’s current population. The crazy thing being that most of modern antibiotics which can be used to successfully treat plague victims, are a recent occurrence as of the 1970’s and onwards.
You might wonder how the Europeans almost 670 years ago in the middle ages combatted such a scourge, especially after losing upwards of 60% of their entire population.
In the 14th century modern antibiotics did not exist. A combination of self-quarantine, reduction of travel, and the disease killing a critical portion of both rat and human populations are all theories as to why the disease declined. This outbreak could have been subdued through pest control. The best course of action would have been extermination and removal of rats whose population had grown to large proportions in the crowded and unsanitary congested cities of 14th century Europe. Once rats are taken out of the equation, the fleas that carry the bacteria which cause the plague are also removed.
Now the bubonic plague is an outbreak of the past, however cases are reported in the U.S. on a yearly basis. The fleas that carry the plague bacterium still exist and are present in nature. The main reason you no longer see such cases in cities is due to pest control of rodents and modern sanitation practices. So the cases that do occur are generally outdoors. For instance, recently you may have heard of the little girl that contracted the bubonic plague in Yosemite last year. She had encountered a dead chipmunk, was bitten by the fleas still on it, and contracted the plague. Squirrels and chipmunks are actually rodents. Most of modern cases these days for the plague follow around these lines, people encountering wild animals that should best be left alone.
Fleas are a great lesson in the worth and importance of modern pest control practices. You wouldn’t think controlling rodents could save the world, but a bite from a flea could prove you wrong.