The Flea

ith three pairs of legs in the adult condition. The reader will best understand the position which fleas occupy in the general classification of animals by remembe

1) Insects, the arthropods, or jointed animals, include (2) Crustaceans, such as crabs, lobsters, shrimps, wood-lice, water-fleas and barnacles; (3) Myriapods, such as centipedes and

is they resemble certain worms which are far less highly organised. The body is elongated, symmetrical on either side, and the mouth and anus are at opposite ends. There is, however, an important advance on the segmented worms. Each typical segment carries

ages, these appendages have been astoundingly modified in form and in function. So it happens that we find in the arthropods of the present day pairs of antenn?, of mandibles and other mouth-parts, of pincers, of legs, of swimming-feet and

cent from the ancestral arthropod; but the relationship of fleas to other insects living at the present day is of more immediate concern. Insects are highly specialized arthropods and fleas a

ef in the special creation of the various species of animals now living on the earth and have conclusively shown that they have arisen by descent and modification from other f

y unlike any other living insects to deserve a place in an order by themselves. To this order the name Siphonaptera has been given: which means that the insects comprised in it are provided with sucking mouths and are destitute of wings. Another name for the order is Aphaniptera, but this is gradually falling into disuse. Linn?us (1758) only mentions two species of flea: the human flea which he appropriately named Pulex irritans, and the chigoe of hot countries which he called Pulex penetrans, from the habit which the female has of burrowing und

gists have disputed with considerable vigour. Some see the nearest relatives among the beetles, others among the flies. The majority, as we shall see later on, would

rally hatch in a few days, and a minute, white, wormlike larva emerges (Fig. 1). The larv?, of some, and possibly of all, fleas are provided with a wonderful adaptation in the shape of an egg-breaker or hatching-spine. This is a thin plate, like the edge of a knife, where the point of the head comes in contact with the shell. The movements of the prisoner make a slight split in the egg-shell, which then bursts asunder. This organ has vanished in later larval life, and it is probably lost after the first moult

the head are the antenn? and on the upper part of the head is shown the knife-like edge of the egg-bre

laces where the perfect insects will have an opportunity of finding a host as soon as they leave the pupal envelope. The nests of their hosts where the young are being reared are always favourite places. It seems possibl

7 hatched on October 19. The larva spun its cocoon on October 25 and the mature flea emerged on November 2. In North

nest, of the mammal or bird which serves them with blood. In this respect there is considerable difference in the habits of different species of flea. Some attach themselves to an animal

t. Thus man is the true host of Pulex irritans; the cat family are the true hosts of the cat-flea (Ctenocephalus felis); and the dog family are the true hosts of the dog-flea (Ctenocephalus canis). But the human flea is sometimes found on cats and dogs, and cat and dog-fleas occasionally bite human beings; and cat-fleas are found on dogs and dog-fleas are found on cats. All fleas, so far as we know, may occasionally pass from one species of host to another; but they do not, for the most part, seem to flourish in unaccustomed q

x the ingenuity of the collector to solve. Bird-fleas are sometimes found on bats, and this may be obviously attributed to the bats having inhabited a hole which was tenanted by starlings or an old loft infested with the fleas of pigeons. All beasts of prey are sometimes found to harbour the fleas of animals they have devoured. Rabbits' fleas are

eas from the house-martin and the sand-martin are quite different; those from the domestic fowl and the domestic pigeon are distinct species. The causes

ny species of different flea. Some species are very abundant and infest the nests of many different birds. Others are extremely rare. One of these rarities (C. vagabundus) is found in the nests of puffins and other sea-birds. Another has been collected on

of house-martins; yet the nests of these birds are infested with common spe

ve been found in the British Islands,

certain orders of animals. To some extent this is already seen to be the case. The fleas indigenous to the New World are distantly related to those of the Old World. Broadly speaking the geographical distribution of the parasite must follow that of the host. But so

t is probable that it has travelled ov

ger of catching an occasional human flea from the people who crowd round their cages. These are remote contingencies which may happen to anyone. Healthy wild monkeys are much too clean and active to harbour fleas. When they search one another's fur

ats and the ordinary smaller insect-eating bats. The geographical distribution of some bat-fleas is puzzling. For instance, one species (Ischnopsylla unipectinata) is fo

. This great order of mammals includes a variety of hoofed animal

es has been found on camels and horses in Transcaucasia; another on roe-deer in Northern China. The female of the last is often found ensconced on the inside of the nostrils of the deer. O

rcupines, squirrels, rats, mice and a vast number of other small mammals whose geographical distribution includes almost the whole of the habitable glob

epedia, or seals, sea-lions and w

bably have preyed on them. The thorax of these fleas is much reduced and very small in size. Their piercing organs are slender and weak, but they possess enormous spines on the legs with which they hold on to their hosts. These two South American fleas (M. grossiventris and M. andr

e order of pouched mammals before they became divided into the American and Australian groups. Fleas have been c

ing the most aquatic kinds, fleas of

poisonous snakes and is allied to the cobras. The Brown Snake is a terrestrial snake, and one must regard the presence of the flea on such a host as a rare and chance occurrence. The snake was captured at Herdman's Lake, near Perth in West Australia. The same species of flea has also been obtained from the phalangers (Trichosurus) which live

get infested with the fleas of their prey. This change of hosts which is always occurring makes it impossible to draw conclusions from material collected in zoological gardens where many animals are herded together. In menageries, too, the normal conditions of breeding are absent. A German naturalist collected 2036 fleas from theatres, conc

at those from the west of any great region cannot be picked out and distinguished from those obtained in the east. So we also get northern and southern forms of the same species varying slightly. These variations are perceptible in many forms of insects, and

can already be seen in a few species. In the meantime the study of variation must be postponed until collectors have amassed a more plentiful amount of mat

naptera can be divided into three groups or families: (1) the chigoes and their allies, which are the most parasitic fleas (Sarcopsyllid?); (2) the typical fleas to

enormous antiquity stretching back to Permian or Carboniferous ages. The fossil record is most meagre. If we reject as too doubtful the supposed remains of a flea from the lower Oligocene strata at Aix in Provence, only one undoubted fossil has been discovered. Nor does it seem certain that fleas are entirely restricted to preying on vertebrates. Dr Dampf introduced a number of c

? which ultimately turned into fleas, probably Pulex irritans. These fleas, being confined without other food, were observed to prey on the Lepidopterous larv? and to feed freely on their juices. The larv? which were

ch swarm in the dwelling-houses of Corsica, for want of other nouri

in the collection of Professor Klebs. The first point to note is that a flea of this antiquity hardly differs from the existing insects of the present day. It has been referred to an existing genus (Pal?opsylla) of which there are at least four species living. Three of these are parasites of the mole, and the fourth is found on shrews. There is good reason to suppose that the host of the fossil was some insectivorous mammal. The early specialisation of fleas is strikingly illustrated. This

discovery that fleas are connected with the spread of plague is an instance of apparently unprofitable scientific labour proving of direct advantage to mankind. An accurate knowledge of the structure and habits of fleas is now seen to be of importance to all who are engaged in fighting on