Beneficial Animals, &c.
( Originally Published 1915 )
Birds. The Testacella Slug. Earthworms. Centipedes. Beneficial Insects. The Isle of Wight Bee Disease. Literature bearing upon Economic Zoology.
Beneficial animals are on the whole less widely known than injurious species and, unlike the latter, they should be encouraged so far as may be possible and under no circumstances be destroyed. BIRDS occupy a very high place as benefactors of the farmer and horticulturalist. There are a number of kinds which cause little harm, and are in many cases, directly beneficial. Among these may be cited the Field fare, Hedge Sparrow, Wrens, Long-tailed and Coal Tits, Wagtails, Pipits, Swallow, Martins, Swift Cuckoo, Plover, and many others. Tits, for instance, are particularly partial to Scale Insects, as well as Aphides and other Insects. The Willow Wren devours large numbers of various In-sects, and Newstead records one whose crop was filled with larvae of the Winter Moth, another with Aphides, and three other individuals contained large numbers of Fly Maggots. Pipits, the Cuckoo, and Swift are also prominent devourers of Insect life. Occasionally, how-ever, one or other species may be observed devouring fruit, the Mistle Thrush, for instance. but I believe in such cases the small amount of harm they cause is negligable compared with the benefit they confer. In this country much could be done along Continental lines to-wards encouraging beneficial Birds, especially by means of nesting-boxes, which help to ensure their presence in desired areas. The Department of Economic Zoology in this University has achieved some good results in the larch plantations of the Manchester Corporation catchment area around Lake Thirlmere. Here the Larch Saw-fly is most destructive, and by fastening on the trees large numbers of nesting-boxes suitable for Tits, which prey on the larvae of this Insect, direct benefit has resulted.
Among MOLLUSCS the carnivorous Slug Testacella alone is valuable. It is a dirty white or yellowish form with a small shell situated at the hinder end of the body. In injurious Slugs the remains of the shell is always very far forwards and in close relation to the respiratory pore. It is local in this district, but has occurred in several localities. Testacella feeds upon other Slugs, Worms, and dead animal matter, and causes no harm to vegetation.
EARTHWORMS are true segmented worms and differ from Eelworms. In the course of burrowing Earth-worms let in moisture and air, the subsoil becomes loosened, and direct benefit therefrom is derived. Large quantities of earth are swallowed by them, which they pass out of their bodies in the form of "worm casts," commonly seen on lawns and flower-beds. In this manner fresh soil is constantly being brought to the surface, and at the same time Earthworms draw numerous leaves and other kinds of vegetation into their burrows which they consume in appreciable quantities. Humus is partly due to the activities of Earthworms—the bringing of soil to the surface and the burying of vegetable material is an important factor in the humus formation, which adds to the general fertility of the land. Darwin calculated that as much as ten tons of soil per annum passes through the bodies of Earthworms and is brought by them to the surface, over each acre of good land.
MILLIPEDES belong to the class of Myriapoda which are more closely related to the Insecta than to any other group. Like the Insects, Myriapods are provided with a single pair of feelers or antennae, but they always possess more than six pairs of legs, usually a large number, and never acquire wings. The two main groups of the Myriapods are the Centipedes or Chilopoda and the Millipedes or Diplopoda. The former, which are beneficial rather than injurious, have a somewhat flattened and a single pair of legs to each segment. So far known they feed upon small worms, slugs, insect etc., and also upon dead animal matter. The Milliles may be readily recognised by the possession of two sets of legs to each body segment. They occasionally are injury to potatoes and other root crops, and are not known as " false wireworms."
(Coccinella septempunctata). Both as larvae and adults Lady Birds devour great numbers of Aphides and Scale Insects, and for this reason they should never be destroyed. The females deposit their eggs as a rule on Aphid infested plants so that their larvae may not have far to wander for their food supply. The Beetles are all very similar in shape and are mostly black and red, or black and yellow in. colour. They hibernate during the winter beneath bark of trees, under rubbish and in outhouses, etc. In the following spring they lay their cream-coloured eggs closely packed together in groups. The larvae are black or leaden-coloured, marked as a rule with yellow or orange. They crawl freely about the plants and consume great numbers of Aphides and other Insects. The pupa are attached to the upper or undersides of the leaves and are broad black objects marked with cream-colour or yellow. The adult Lady Birds
appear early in summer and are common objects of the field and garden throughout the season. It is note-worthy that the destructive Scale Insect Icerya purchasi which devastated the orange groves of California has been almost entirely destroyed and checked by the importation into America of an Australian Lady Bird Novius cardinalis. The Scale Insect has thus remained permanently controlled, and the Novius Beetle is now a regular resident in California. The orange Scale Insect has been controlled by a similar measure in Florida, New Zealand, Portugal, Cape Colony, Formosa, Egypt, France, and other countries. HOVERER FLIES belong to the family of the Syrphidae They are often brilliantly coloured, being black with yellow bands, and have the appearance of small Wasps. They hover in the air, remaining stationary, except for their vibrating wings, over one spot for several minutes and then, darting away suddenly, hover again over a fresh spot. They only fly in sunshine, and rest on leaves and flowers in dull and wet weather ; they feed mainly upon nectar. Most species of Hoverer Flies lay their eggs among- colonies of Aphides, and their maggot-like larvae on emerging feed voraciously upon the latter. When fully fed the pupae are to be found enclosed in membraneous puparium on the leaves and stems of plants close to where the larvae lived. The greater number of the members of this family are, therefore, beneficial Insects.
ICHNEUMON FLIES and their allies are parasitic Insects belonging to the order Hymenoptera, and are related to the Bees and Wasps. They can be recognised by the presence of four transparent wings, and by the possession in the female of a long needle-like ovipositor or egg-laying instrument. Almost every species of Insect is preyed upon by some other species of Ichneumon Fly or its ally. By means of their ovipositor these Insects pierce the skin of other Insects and lay their eggs within the body of the latter. The host Insects are not killed by this operation, but continue feeding. The larvae of the parasite hatch out in due course and gradually devour the blood and tissues of the host, avoiding, however, the vital organs until the very last. The parasite turns to the pupae either within or outside the host Insect, and just about the same time the latter dies. Some Insects are greatly destroyed by parasites and thus kept in check naturally—the common Hawthorn Scale and the Gypsy Moth are familiar examples. In America, however, the Gypsy Moth has got introduced artificially, and has now spread with alarming rapidity and causes millions of dollars damage annually. Unfortunately the natural enemies of this Moth were not imported, and the U.S. Department of Agriculture recognise that the only way of ridding the country of this Insect is by importing its natural enemies or parasites from Europe. This work is now steadily going ahead on a very large scale, but it is too early to know the final result. In Italy mulberry cultivation has been threatened by a Scale Insect. Diaspis pentagona. In 1891 the pest assumed such serious proportions that the Italian Government passed a legislative measure compelling mulberry cultivators to use all avail-able means for coping with it. This, however, proved of little efficacy, and it was not until Professor Berlese, of Florence, introduced great numbers of a minute parasite from America into Italy that much headway was made. From all later reports it appears that this parasite has acclimatised itself to Italy and is proving of great value in destroying the Mulberry Scale.
Of all beneficial Insects the Hive Bee is the most useful species. It is desirable here to make some reference to the Isle of Wight Disease (IS), which is causing much mortality among apiaries all over the country. The epidemic is due to a minute Protozoan organism (Nosema apis), and the disease is spread by the distribution of its spores among unaffected bees. The disease is primarily one of the digestive system, and affected Bees arc, as a rule, unable to fly more than a few yards without alighting. As the disease progresses the Bees can only fly a few feet from the hive, and then drop and crawl aimlessly over the ground. They may often be seen crawling up grass stems or up the supports of the hive. Diseased Bees frequently lose their power of flight, their abdomens become greatly distended, and often the wings are " out of joint," the hind wings' protruding upwards and outside the anterior pair. In bad attacks large numbers of diseased Bees are to be found clustered together within the hive, or on the alighting board and ground. Some-times the symptoms resemble those of " Bee paralysis " or of " dysentry," but nevertheless the disease is quite distinct from either of these complaints. The spores of the disease are spread in various ways; thus water near the hives becomes infected with Bee excrement, containing the spores,, which arc liable to be imbibed by the next Bee which visits the same spot. Honey, pollen and wax also become infected with the spores in a similar manner, and are very fertile sources for spreading the disease,. Infection from one hive or apiary to another can be effected by the sale of diseased swarms, by the robbing of a diseased colony by healthy Bees, and by swarms occupying hives which were formerly infected. Bad weather also. encourages the spread of the complaint, as the bees do not then take cleansing flights. There is evidence to indicate that partial immunity of stocks happens. Such stocks, however, might be hard to recognise, and at the same time would act as sources of infection for susceptable colonies. As regards measures against the disease, healthy stocks should be removed from the neighbourhood of diseased hives. Clean water should be readily accessible, changed daily and protected from contamination. The usual drinking places should, if possible, be done away with. All dead. Bees should be burnt and diseased colonies, including the queens, destroyed. The ground around the hives should be dug over and treated with quicklime. Infected hives and all utensils should be charred inside and out with a painter's lamp. In place of charring a very thorough application of formalin or carbolic acid may be used, and the hives afterwards properly aired in strong sunlight. No cure for the disease has so far been discovered. The. problem of hereditary infection is of great importance, but I am not aware that any evidence thereon is yet forthcoming. If the queen is capable of transmitting the Nosema parasite to the eggs, the young brood would thus be born infected, and the disease be passed from one generation to another, as happens in the case of the Nosema which causes Pebrine in silkworms. Investigations along these lines are greatly needed.