FLEAS
The fleas used to be considered as degenerate Diptera and were placed with that group but they are now classed as a separate order (Siphonaptera). Within recent years these little pests have come into special prominence on account of their importance in connection with the spread of the plague. The fact that they are so abundant everywhere and that they will so readily pass from one host to another makes the possibility of their spreading infectious diseases very great. Besides the kinds that are concerned in the transmission of plague, which are discussed in another chapter, there are many other kinds infesting various wild and domesticated animals and a few attacking birds.
One of the most important of these is the jigger-flea or chigoe (Dermatophilus penetrans, [Fig. 33]). Various other names such as chigger-flea, sand-flea, jigger, chigger are also applied to this insect as well as to a minute red mite that burrows into the skin in much the same way as the female of the flea. So although they are entirely different creatures you can never tell from the common name, whether it is the flea or the mite that is being referred to. Both the male and female jigger-fleas feed on the host and hop on or off as do other fleas, but when the female is ready to lay eggs ([Fig. 34]), she burrows into the skin. Her presence there causes a swelling and usually an ulcer which often becomes very serious, especially if the insect should be crushed and the contents of the body escape into the surrounding tissue.
These little pests are found throughout tropical and subtropical America and have been introduced into Africa and from there have spread to India and elsewhere. They attack almost all kinds of animals as well as many birds, being of course a source of great annoyance and no inconsiderable loss. They are more apt to attack the feet of men, especially those who go barefooted. Sometimes they occur in such numbers as to make great masses of sores.
On account of being such general feeders they are difficult to control, but some relief may be obtained by keeping the houses and barns as free as possible from dirt and rubbish and by sprinkling the breeding-places of the pest with pyrethrum powder or carbolic water. Those that gain an entrance into the skin should be cut out, care being taken to remove the insect entire.
BEDBUGS
In the order Hemiptera, or the true "bugs" in an entomological sense, we find a few forms that may carry disease. The bedbug ([Fig. 35]) (Cimex lectularis) has been accused of transmitting plague, relapsing fever and other diseases. Very recent investigations show that the common bedbug of India (Cimex rotundatus) harbors the parasite that causes the disease known as kala azar, and there is no doubt that it transmits the disease.
LICE
The sucking lice ([Fig. 36]) which also belong to this order are suspected of carrying some of these same diseases. It is thought that the common louse on rats (Hæmatopinus spinulosus) is responsible for the spread from rat to rat of a certain parasite. (Trypanosoma lewisi), which, however, does not produce any disease in the rats, but if they are capable of acting as alternative hosts for such parasites, it is quite possible that they may also carry disease-producing forms.