The common small white butterfly of Europe (Pontia or Pieris rapae) is now established in North America; and the march of the jigger, or foot-infesting flea (Sarcopsylla penetrans) of tropical America, across Africa, has taken place in quite recent years.
A B In Great Britain the flea beetles (Halticidae) are one of the most serious enemies; one of these, the turnip flea (Phyllotreta nemorum), has in some years, notably 1881, caused more than 500,00o loss in England and Scotland alone by eating the young seedling turnips, cabbage and other Cruciferae.
Guinea-pigs set free in plague-infected houses become infected with the rat flea and develop plague in a certain percentage.
The report also considers it proved that the bacillus pestis multiplies in the stomach of a flea and may remain a considerable time within its host.
It was also shown that animals may become infected through the faeces of a flea which has been fed on plague-infected rats.
As to how they convey it from man to man the greatest probability is in favour of the flea as an intermediary.
Healthy rats contracted plague from infected rats when the only apparent means of communication between the two was the rat flea (pulex cheopis).
The gad-fly (abu), the housefly (hai), the mosquito (ka), the flea (nonzi) and occasionally the bedbug (called by the Japanese kara-mushi because it is believed to be imported from China), are all fully represented, and the dragon-fly (tombO) presents itself in immense numbers at certain seasons.
He even noted the fact that the pupa of the flea is sometimes attacked and fed upon by a mite - an observation which suggested the well.
The human flea is considerably exceeded in size by certain other species found upon much smaller hosts; thus the European Hystrichopsylla talpae, a parasite of the mole, shrew and other small mammals, attains a length of 5z millimetres; another large species infests the Indian porcupine.