Fig. 60.—The Japanese variety of Haemadipsa zeylanica. × 1. (From Whitman.)
In the East, where many of our Territorial regiments are now stationed, we come across another species of leech even more injurious to mankind than Limnatis nilotica. This Asiatic leech is known as Haemadipsa zeylanica, and is one of a considerable number of leeches which have left the water, their natural habitat, and have taken to live on land.
From India and Ceylon, throughout Burma, Cochin China, Formosa to Japan, the Philippines, and the Sunda Island, this terrible, and at certain elevations ubiquitous, pest is spread. It lives upon damp and moist earth. The family to which it belongs is essentially a family which dwells in the uplands and shuns the hot, low-lying plains. Its members do not occur on the hot, dry, sandy flats. Tennant has described the intolerable nuisance they are in Ceylon. In fact of the many visible plagues of tropical Asia and its eastern islands they are perhaps the worst. Yet few have recorded their dread doings, and those few have escaped credence.
Fig. 61.—Haemadipsa zeylanica, seen from above. × 2. (From Blanchard.)
Each specimen of Haemadipsa zeylanica is of a clear brown colour with a yellow stripe on each side and with a greenish dorsal stripe. There are five pairs of eyes, of which the first four occupy contiguous rings; but between the fifth and seventh ring there are two eyeless rings interposed. As in the medicinal leech there are three teeth, each serrated like a saw.
In dry weather they miraculously disappear, and nobody seems to know quite what becomes of them; but with returning showers they are found again on the soil and on the lower vegetation in enormous profusion. Each leech is about one inch in length and is about as thick as a knitting-needle. But they contract until they attain the diameter of a quill pen, or extend their bodies until they have doubled their normal length. They are the most insinuating of creatures, and can force their way through the interstices of the tightest laced boot, or between the folds of the most closely wound puttee. Making their tortuous way towards the human skin, they wriggle about under the under-clothing until they attain almost any position on the body they wish to take up. Their bite is absolutely painless, and it is usual for the human sufferer to become aware that he has been bitten by these silent and tireless leeches when he notices sundry streams of blood running down his body when he at last has the opportunity of undressing.
Fig. 62.—Haemadipsa zeylanica. Head, showing the eyes and the serrations of the jaw. Highly magnified. (From Tennant.)
Sometimes, as Tennant’s figure shows, these land-leeches (H. zeylanica) rest upon the ground. At other times they ascend the leaves of herbs and grasses, and especially the twigs of the forest undergrowth. Perched upon the ends of growing shoots, leaves, and twigs, stretching their quivering bodies into the void, they eagerly watch and wait the approach of some travelling mammal. They easily ‘scent’ their prey, and on its approach advance upon it with surprising rapidity in semicircular loops. A whole and vast colony of land-leeches is set in motion without a moment’s delay, and thus it comes about that the last of a travelling or prospecting party in a land-leech area invariably fares the worst, as these land-leeches mobilise and congregate with extraordinary rapidity when once they are warned of the approach of a possible host, but not always in time to engage in numbers the advanced guard.