ON COLLECTING AND PRESERVING FLEAS

There are two methods by which fleas may be preserved for study when they have been collected. The first is by keeping the specimens in small tubes of alcohol; the second is by mounting each in Canada balsam on a slide for the microscope. The advantage of the former method is that the material can be used for dissection. The student can do nothing without a microscope, though some of the commoner species can be identified with tolerable certainty by a practised eye which is assisted by a pocket-lens.

The tubes are best stored away in a cabinet fitted with wooden shelves and holes to take the tubes like a test-tube holder. Fleas dried and preserved loose in a box, or gummed on card, are useless for purposes of minute examination, and are soon destroyed.

Fleas may be collected from the great majority of mammals and birds in almost all parts of the globe. They can be found in the hair and under the feathers, and also in the places where the animals habitually sleep. The best places, from which a plentiful haul may often be obtained, are the holes and nests in which the young have been reared.

It is essential to remember, when an animal has been killed, that all the fleas leave as soon as the body of the host gets cold. No time, therefore, should be lost in searching for specimens.

If the animal is small enough it may be put into a cardboard box, or a white linen bag, and a few drops of chloroform or benzine can be poured on it. In a short time the fleas will be found dead in the bag or at the bottom of the box. Some may also be found in the hairs and feathers when they are turned back.

In the case of a large mammal the hair must be turned backwards shortly after death, when the live fleas may be seen running about and caught. For this purpose a small camel’s hair brush is very useful. If a flea is touched with a brush of this kind which has been dipped in chloroform, benzine, or alcohol, the insect sticks to the brush, but can be easily floated off into the tube of preservative. The best preserving liquid is 50 per cent. alcohol. Methylated spirits can be used. Acetic acid can also be used; but it is objectionable because in a short time it destroys the corks of the tubes.

Each tube should only contain the fleas collected from one host, but as many specimens as possible should be secured, because there may be several species of flea on the same host.

The tube must be securely corked and labelled, with the date, the locality, and the name of the host. In foreign countries it may not be always easy to do this. In such cases the skin of the host must be preserved with the tube for subsequent identification. A number corresponding to the label on the tube should be attached to the skin of the host.

Fleas collected without records of the host from which they were obtained are of little or no scientific value. For this reason a tube should contain the parasites of one host only.

A convenient way of preserving records temporarily is to write in pencil on a small piece of paper which can be rolled up and put in the alcohol in the tube.

Small mammals generally, including bats, are good hosts; Rodents and Insectivora afford usually the most fruitful captures. In trapping mice and voles only those traps should be used in which the animals are caught alive, or the fleas will have left their hosts before they can be secured and examined. Field-mice caught in the ordinary small penny mouse-trap are often found dead in the morning. The best traps are made on the principle of the ordinary mouse-trap, but larger. A piece of bacon-rind on the hook is a good bait for almost all small mammals. Where a number of traps are put down and left out they should, of course, be visited daily.

When a live mouse, or other small mammal of similar size, has been captured it may be transferred from the trap into a small white linen or holland bag. The animal can then be killed by tapping its head or breaking its neck from the outside of the bag. After this has been done, fleas may be searched for in the fashion described above.

Most of the small mammals which act as hosts for fleas are nocturnal. The localities where they may be trapped are numberless, but only a small proportion of the captures may yield anything for the flea-collector. I have heard of a collector of small mammals who travelled through remote parts of Spain and never lost an occasion for putting down his traps when he had to change trains at a country railway junction. In England it would, however, seldom be worth doing this, as, on many lines, there is an attempt to make the arrival of one train and the departure of another correspond.

The following plan for securing bird-fleas will be found successful. The nests of birds should be taken as soon as the young are fledged and flown. If the nest is small it can be put into a glass-topped box lined with white paper. If too large, the whole nest, or the most firmly matted and dirty part, may be put into a glass globe (such as gold-fish are kept in) and a piece of paper tied over the mouth. From time to time the nest should be slightly damped with water. In every case a label should be put into the receptacle to preserve the name of the bird which built the nest. The bottom of the nest may sometimes be seen to be full of the larval fleas; but in any case fleas will probably emerge from pupÆ. The fleas will continue appearing for as much as six weeks or eight weeks after the young birds have left the nest. They must be watched for and taken off the sides and top of the box with a camel’s hair brush dipped in chloroform or benzine. I have seen dozens of fleas come from the nest of a tit (Parus major) in the course of a few weeks. They were all of the common species (C. gallinÆ). When the lid of the box is removed it is difficult to prevent a few escaping in the room, but I have never known them cause inconvenience to anyone.

Collectors in warm countries should give their attention to the chigoes and their allies, which are of great interest and have been little studied. They are found on mammals and birds in tropical and semi-tropical countries. The males are very difficult to find, but the females are large and very parasitic. They have the appearance of a small wart firmly fixed to the skin. Small mammals may be transferred, with their chigoes attached, to a bottle of alcohol. Many examples of these insects are often found together on the more naked portions of their hosts.