In Touch With Nature

Hawke's Bay Tribune, Volume XVII, 1 October 1927, Page 11

In Touch With Nature

(By

J. DRUMMOND,

F.L.S., F.Z.S.)

Nature notes appear In the "Tribune" every Saturday. Mr Drummond will be pleased to rerooelve from our readers, notes relating to any remarkable Incldont or peculiarity they have noticed tn bird, animal, or plant life, and he will also be pleased to answer questions. Letters should bo addressed to him personally, oaro of Tribune Office, Hastings. GNATS, MIDGES, AND MOSQUITOES A bottle of specimens sent by Mr. D. N. Hay, Matamata, 120 miles south of Auckland City, has gone astray, but bis description of the creatures which interested him and which he imprisoned in the bottle leaves no doubt as to their identity. He States: “Thev looked like a mass of red worms. They were in a bunch on the edge of the running water of J a drain on a farm. They seemed to ' be sensitive to sound or vibration, as the snapping of fingers over them caused them to hunch up into a tighter mass. The specimens were removed from the water on September 10, and *t the time of writing, September 12, thev were still very much alive. They were noticed here only once before at this time of the * year in 1925." GRUBS OF A GNAT. Tbey are blood-worms, but are not worms. Their title n merely a popular one, bestowed on account of their appearance; and appearances in this case, as in many other caaes. are misleading. They are the grubs of a Sat probably the harlequin gnat, rionomus: in the Greek it. means moving hands and gesticulating, as in a pantomime. The eggs are deposited in strings surrounded by mucous. Many of them are so transparent that, with the help of a microscope, there may be traced in them the development of the embryo, a very fascinating process. The little blood-worms are aquatic. Their colour is caused bv haemoglobin, the matter of a red colour contained in the red corpuscles of the blood, which has the power of attracting and storing oxygen and giving it off to the tissues as they reouire it. It is stated that some grubs of the harlequin gnat, plentifullv provided with haemoglobin, are able to live at great depths—at even 1000 feet in Lake Superior—and come to the surface only occasionally. A few that tolerate salt water have been brought up from the depths of the sea. The grabs of some species of the harlequin gnat are devoid of haemoglobin, and must live near the surface of the water. As in almost every group of insects Australia has many more species of the harlequin gnat than New Zealand has. There are ten in New Zealand and thirtv in Australia: in the United Kingdom there are about 200. QUEER REPRODUCTION. In one species of harequin gnat, there has been observed a strange form of parthenogenesis— “maiden" and “birth"—the production of offspring from unfertilised eggs. Members of that species lay eggs in the chrysalis stage, before they have become perfect insects. The parthenogenesis is in only the generation that comes in the spring. Development goes on in a natural way in the autumn. The explanation offered is that, when the eggs are deposited, the little creature is practically a perfect insect, but has retained the covering of the chrysalis. A somewhat similar process occurs in a gall midge. Miastor. which occurs in New Zeeland and in other countries. A female of that group lavs a few comparatively large eggs. A grub comes out of each egg. It does not advance in the stage of a perfect insect but produces in its Interior young grabs. These, after consuming the interior of their parent’s body escape by making a hole in the skin. This process of reproduction paedogenesis —“child" and “birth”—means the production of offspring from unfertilised eggs by immature females. It is not quite the same as parthenogenesis. In paedogenesis. the imperfect females do not wait until maturity in order to produce their offspring. This method, it is believed. may be continued for several generations, through autumn, winter and spring until the following summer. A generation of the grubs then goes on to the chrysalis stage, and to the perfect stage. METHODS OF FERTILISATION. In a general way, by some biologists at least, parthenogenesis is believed to exemplify the principle of making hay while the sun shines. It is an attempt to take advantage of a short season of favourable conditions in order to multiply the race as quickly aq possible. No males have been discovered in some species of rotifers and crustaceans, showing apparently. that parthenogenesis may continue indefinitely, without any fertilisation of the eggs whatever. As a matter of fact, recent experiments show that fertilisation of the eggs is not always indispensable, even in casta in which eggs are not naturally subiect to parthenogenesis It c»n be induced artificially. In this wav unfertilised eggs of a sea-urchin developed into young sea-urchins after they were exposed to the action of chemical reagents. The unfertilised eggs of a worm were stimulated to develop into young by the addition of potash and acids. A short exposure of the eggs of the starfish to temperatures between 32 decrees, and 38 degrees Centigrade causeu the development of almost every egg into a free-swimming young starfish. SOME ARE LUMINOUS. Another unusual circumstance connected with the harlequin gnats is that some individuals become luminous. This has been noted particularly in Eastern Europe and Western Asia. The clouds of dancing insects look like a thin phosphorescent haze, drifting wilh the wind. They are fhen included amongst the pill-o’-

the wisps. The luminous condition may be taken on by the whole of the body and the legs, but not by the wings. The theory is that tfie con. dition is a disease caused by bacteria in the gnats’ bodies. New Zealand’s common harlequin gnat. Chironomus zealandicus. may be seen in all parts of the Dominion all the year round. At times it is very plentiful. On warm still days, near Lake Ellesmere, it often for hours together forms vertical columns of surprising height and density. GLOW WORMS OF WAITOMO. There is so little difference between gnats, midges and mosquitoes that some excuse is found for confusion in the use of the names. Gnats and midges cannot be distinguished. They usually are smaller than mosquitoes, but resemble them. One definition is that gnats are mosquitoes and mosquitoes are gnats translated into Spanish, which has adapted the word from the Latin musca a fly. All are true members of the order of the flies, the Diptera. ranking with the house-fly, the blue-bottle, the horsefly. and the daddy-long-legs. It is a gnat—a fungus gnat—that has made the Waitomo Caves famous. Grubs of that gnat are the “glow-worms” that light up the caves like the chambers of a fain- palace. As descrilied by an English entomologist, these beautiful grubs cause “a radiance that absorbs the whole faculty of observation, the radiance of a massed body of glow-worms such as cannot be found anywhere else in the world, incalculable ns to numbers and merging their individual lights in a nirvana of pure sheen." BLOOD-SUCKING FEMALES. In a joint on the antennae of members of the order of flies there is a complex nervous structure known as Johnston’s organ. It is particularly well developed in the harlequin gnata and in the mosquitoes. and is larger in the males than in the females. One entomologist believes that it is concerned with the perception of vibration. To the unaided eye. the grubs of all members of the order are devoid ot any ornament whatever. Only a few species of the order have acquired the habit of sucking blood from the larger and higher animals, and all these insects have suctorial mouths. It is somewhat strange that most of the bloodsucking species have aquatic grubs, or larvae. Stranger still is the fact that the habit is confined to the females. Only the female mosquito stings. The male mosquito, provided with a less effectual mouth-organ, is described as an inoffensive creature. Some students of mosquitoes believe that the blood-sucking of the females is an acquired habit, and that food obtained in this way is not essential to their existence. It is stated that the act often is attended with fatal consequences to the individual insect that commits it.