Flea is the common name for any of the small wingless insects of the order Siphonaptera. Fleas are external parasites, living by hematophagy off the blood of mammals and birds. In most cases, fleas are just a nuisance to their hosts, but some people and some animals suffer allergic reactions to flea saliva resulting in rashes. Flea bites generally result in the formation of a slightly-raised swollen itching spot with a single puncture point at the center. Fleas can act as a vector for disease. One possible example of this was the bubonic plague, which may have been transmitted between rodents and humans. Murine typhus (endemic typhus) fever, and in some cases tapeworms, Hymenolepis, can also be transmitted by fleas.