NATURE NOTES

New Zealand Herald, Volume LXXI, Issue 21396, 20 October 1934, Page 1 (Supplement)

NATURE NOTES

11V ,T. DRUMMOND, F.L.S., F.Z.S

PERSISTENT INSECTS

The Maori hug's intolerable smell arises from glands in the body and from a dark oily fluid ejected from its mouth. Bugs are armed with lancets in their jaws. They do not bite. They suck food. The Maori bug sometimes is called black, beetle. A beetle has hard forewings. These, when in repose, usually fit closely over the back in a straight line and cover the hindwings, which are tissuey and can be used for flight. When a beetle flies it raises its hard forewings. This brings the hindwings into use. On alighting, the hindwings are folded neatly and the forewings drop on to them. The Maori bug is neither a bug nor a beetle, but a cockroach. The smell it makes characterises the whole cockroach family, numerous, primitive, ancient in lineage, extraordinarily persistent in surviving through the ages, and at present cosmopolitan.

New Zealand has only five species of cockroaches in addition to the Maori bug, but this country has been invaded by two notorious species. Like the Maori bug they intrude into dwellings, where they make themselves unpopular. One probably came from the Old Country. The original home of this species has not been discovered. It is not a native of the Old Country, yet it has established itself in every city, town and village there. Popularly it is called the German cockroach. No country claims it. Germany repudiates its citizenship of the Fatherland. Germans call it the Russian cockroach and Russians call it the Prussian cockroach. In America it is called the Croton bug, on account of an association with the Croion Aqueduct, which conveys water' to New York City. The dampness of water-pipes is to the liking of this species. Pressure of the water carries individuals long distances in pipes without injury. Completion of the Croton waterworks gave it entrance to New York houses, and facilitated its increase and distribution.

The other introduced species is the American cockroach, a native of tropical America. This species is fond of the sea apparently, as it often is found on vessels. ],t is more plentiful in seaport towns than inland, does not enter dwellings as readily as its ally does, and favours warehouses, breweries, greenhouses and places of that sort. The German cockroach is somewhat slender, half an inch long, dark yellow or light brown. The American cockroach is broader, an inch and a half long and reddish-brown.

Very interesting is Mr. F. Laing's record, in a British Museum publication, of these insects' life history. It begins with a female laying eggs, united in a horny case. There may be as few as twenty-eight eggs in a case, or as many as fifty-five. The case is formed in the female's body, and is retained until the young are ready to be hatched. In time it is rent along a ridge on top. The two halves gape apart. The young cockroaches, appearing head first, struggle from the case. No sooner are they born than they run about actively, little white cylinders, each carried on six long legs. Their bodies begin to flatten and to broaden, the white is replaced by grey, the grey by brown. Growth is rapid. About a week after birth a series of moults begins. Six weeks after birth the youngster becomes a nymph, resembling an adult in every way except development of wings. Six weeks later it reaches maturity.

Loving darkness, it hides during the day and comes out at night. If a light is turned on suddenly in a room it occupies at night it seeks shelter in a cranny, running swiftly. It feeds on paper, on the whitewash on walls, books, boots, hair, leather, dead animal matter, and sweet stuff. It likes beer. Hiding in bales of goods, it gains an entrance to warehouses. Furniture, groceries ' and linen from laundries may help it to get into dwellings. Mr. Laing has failed to discover satisfactory evidence to . convict cockroaches of spreading disease, although they are well qualified to- do so, but he is afraid that further research may incriminate them as deeply as the common housefly-

In spite of insect powders, sprays, poisons, fumigation and traps, cockroaches flourish. Many cockroachtraps are on the English market. The usual baits are bananas and beer. Twelve traps, baited with bananas and beer, meat and vegetables and aniseed solution, were placed in a building in England. During fifteen weeks 8430 cockroaches were caught. The chief difficulty is that cockroaches are shy, wary and suspicious, and much more intelligent than they appear to be. They seem to know when a housewife is after them and when arsenic is laid for them.

Their family history has been traced in pages of stone to Silurian times, estimated at 400,Q00,000 years ago. Their devices to escape from enemies may explain in part their success in life. A test of their intelligence showed that they have sufficient sense to learn from experience. Cockroaches were placed in a cage divided into two chambers, one light, the other dark. Disliking the light, they sought the dark chamber. There was an electric apparatus in it, and when a cockroach went from the light chamber to the dark chamber it received a shock. They soon learnt that the dark chamber was undesirable, and they stayed in the Jight" chamber putting up with the glare. Males learnt more readily than females. .

To an eminent American entomologist, Dr. L. O. Howard, cockroaches are free-lances, invaders and feeders on many things in dwellings, typical of the ability of insects as a class to adapt themselves to different sorts of foods. Dr. Howard, in " The Insect Menace," prepared a list of sixty-five substances valuable to human beings and to insects. Insects, he points out, are not sufficiently intelligent to invent tools, but their needs have developed their own parts into very useful tools. An insect's legs are adapted tcHhe special methods of life the insect follows. It may have legs for running, legs for jumping, legs for grasping, legs for swimming or legs for digging. Different legs belonging to a single insect may bo used in a different way. The front pair may be used for grasping or digging, the others for walking. Molecrickets live mostly underground.

Concentrated study of insects' senses has not given extensive results. The general line of investigation is on a faulty assumption that an insect is in every way made on the same plan as a person. An insect's brain is primitive in structure. An insect can hear. It may pick up sounds by an apparatus on its legs, on its feelers, or on its body. Some insects are hypersensitive to the scents of flowers. Their sense of touch is delicate. Their large compound eyes, which lia/e many small surfaces, cannot be closed or moved, and people do not know the nature and extent of their vision. There are many things in the insects' world that human beings can never understand or know of.