Migrating Animals
Bed mites can latch themselves onto migrating bats or migrating birds. Wherever that animal flies to, so do the bed mites.
Migrating People
The Mayo Clinic states that bedbugs can stow away in people's luggage or sleeping bags, and then crawl off to wherever that person travels. This is one reason why bedbugs are often seen more in hotels than in private homes.
Elimination of DDT
The Mayo Clinic also states that with the banning of the toxic pesticide DDT, bed mites are increasing in numbers. However, there are far less toxic ways to kill bed mites than DDT.
Fast Moving
According to CNNMoney.com, bed mites move so quickly that if one apartment is being fumigated, they simply move to another apartment. This is why exterminators recommend entire buildings need to be done at once.
Misconceptions
Bed mites do not transmit diseases, but the bites themselves are bothersome enough.