NATURE NOTES

New Zealand Herald, Volume LXXI, Issue 21769, 7 April 1934, Page 1 (Supplement)

NATURE NOTES

WATER BEETLES' HABITS

BY J. DRTJMMOND, F.L.S., F.Z.S,

On Mr. T. Hodgson's farm, North Auckland, there are water-tanks and troughs for cows to drink out of in the summer. In rainy weather a munga is kept full of water. Beetles are seen coming to the surface of all the water to take in air-bubbles. As soon as they have done so, they go down again. While watching them in a tank-trough Mr. Hodgson saw a beetle fly along and drop into the water.. Another came and dropped into the water in the same way. Thinking that they were ordinary black beetles, he caught one, took it out of the water, and placed it 011 a board. After a short time its shining back opened up, and it flew straight into the water-tank. Further experiments showed that all the beetles except an unusually big one could fly.

These are water-beetles, admired for the mechanical perfection of their hind legs, used like oars for propulsion beneath the surface of the water. This structural adaptation meets the requirements of life in the water instead of in the air or on the land. More remarkable is the efficient equipment, mentioned by Mr. Hodgson, for taking in supplies of air. Water-beetles spend most of their time in the water. They take their meals there, eating ravenously. The females lay their eggs there, and there young water-beetles are hatched. Life in the water seems to have been chosen by the water-beetles' remote ancestors, which, probably, lived on the land and breathed air freely. There is sufficient of the old ancestors in present water-beetles to make air essential to them.

They_ love the water, but they must have air. Instead of gulping it in the ordinary way, each water-beetle has an air-reservoirj an airtight space between the hard wing-cases and the back. Feeling the necessity for air, a water-beetle rises to the surface. It opens a chink through which air enters the reservoir. The chink is closed and down the insect dives, to paddle swiftly through the water and chase and devour other aquatic insects. The necessity for air is shown by the fact that, in spite of being at home in the water, water-beetles drown sooner than most land-beetles do.

Another feature of these interesting insects, their ability to fly as well as to swim and dive, was noted by Mr. Hodgson. Their two front wings are cases, useless for flight. They cover and protect the second pair of wings, which function, and with which water-beetles go through the air at a fair speed. The functioning wings are used for individual flights and for a sort of migration. They sometimes carry their owners for long distances, mostly at night. As between one thousand nine hundred and two thousand species of waterbeetles are known, and as lihere are many species that are unknown, especially in colder countries, which are rich in them, they are diversified in several respects, but all are smooth, shiny and oval, carry air-reservoirs and have hind legs modified into oars. Some are very small, others are more than half all inch long.

The .individuals that Mr. Hodgson saw probably belong to the commonest New Zealand species, Rhantus pulverulosus, dull brown, half an inch long. This species is one of eighteen known to belong to New Zealand. Australia has one hundred and eighty-five species.

Roughly, the world's population of water-beetles has been divided into two main groups. One group is flesh-eating in both the grub stage and the perfect winged stage. The other is flesh-eating in the grub stage, but is mainly vegetarian in the perfect stage. The great diving beetle of the Old Country is about an inch long, three-quarters of an inch broad, and olive-green in colour. The habits and characters sketched in this article are the habits and characters of water-beetles in the Old Country, which have a place in almost every entomological text-book. New Zealand's water-beetles have not been studied closely. They, no doubt, follow lines of conduct laid down by water-beetles elsewhere. The waterbeetles' family name is Dytiscidae.

Mr. Hodgson saw one insect that would not go down. It stayed on the surface of the water, and it always swam on its back. The smooth-curved back, keeled like the bottom of a boat, offering 110 resistance to the water, the insect glided fairly quickly as soon as it was on its back. It seemed to have air all among its legs. This is not a beetle, but a water-bug. There are many different species of insects in the order to which bugs belong. All are characterised by a sucking beak, fixed, to the underside of the head. In the mouth-parts there is a sheath, and in the sheath there are slender piercing instruments. Sucking is the result of a pump action. Another pump, according to Dr. R. J. Tillyard, forces saliva into the beak, from which it is injected into a wound. The water-bug that Mr. Hodgson saw is a member of a group with the official title Notonecta. The meaning 0? this is back-swimmer, and members of tho group are popularly called back-swimmers, or water-boat-men. Members of an allied family also are called water-boatmen, as they row with their hind legs. Back-swimmers are adopt divers. They store air needed for breathing in two troughs beneath the abdomen. The air is kept there by special hairs. The young of mosquitoes and of other semi-aquatic insects provide back-swimmers, with food. The water is their birthplace. Tissues of water-weeds are their cradles.

In frosty weather, during the past winter, ground larks, . sparrows and hedge-sparrows entered Mr. P. Crosby's tent at Baton, fifty-three miles northwest of Nelson, where he is mining for gold. Every morning all through the winter they accepted bread-crumbs he offered them. Snow and very heavy frosts make things hard for birds in winter in that district. Hundreds of bellbirds are present. They imitate tuis so faithfully that Mr. Crosby sometimes cannot determine a songster's identity. Tuis pick up charcoal and burnt bones in his garden. On his list are wekas, tomtits, wood-robins, morepork owls, kiwis, wood-pigeons, kakas, harrierhawks, sparrow-hawks, blue' mountain ducks, paradise ducks, black shags, Californian quail, kakapos, black teal, grey ducks, kingfishers, fern-birds, shining cuckoos, long-tailed cuckoos, and rifleman wrens. Keas are on the snow-tops. Ked-headed and yellow parrakeets are present, but are scarce. Saddlebacks and native crows aro very scarce. "This is a birds' paradise," Mr. Crosby writes. " Tho North Island has nothing near it,"

A weta found in a forest near the head of the Slate River, Collingwood district, has been sent by Mr. C. Lewis, who has answered a question sometimes asked in respect to wetas that live in burrows in tree-stems. »lie question is how the wetas get out of the burrows after they have gone in. Do they back out? Mr. Lewis believes that they turn round. Every weta's home he examined was enlarged inside sufficiently to allow the weta to turn around. In old burrows there were extensive enlargements and galleries branching from the main halls.