NATURE NOTES

New Zealand Herald, Volume LXX, Issue 21640, 4 November 1933, Page 1 (Supplement)

NATURE NOTES

BY J. DRCMMOND, F.I/.5., F.Z.S

ARMIES OF CATERPILLARS

The caterpillars that have ravished crops in the Ashburton County and other Canterbury districts have been identified as Persectania Ewingii, or Persectania coniposita, known popularly as New Zealand armv-worms. They are the larvae, as entomologists would say, of medium-sized night-flying moths, somewhat drab but not unhandsome, decked in browns and greys, picked out with white. These moths are plentiful in all parts of New Zealand, on Stewart Island, on the Chathams and, doubtless on other islands in the Now Zealand geographical area. Messrs. C. E. Clarke and Stuart Lindsay found them very plentiful at Lakes Manapouri and To Anau.

Tho species hardly could escape the attention of Mr. G. V. Hudson. He has given a portrait in colours of a female in " The Butterflies and Moths of New Zealand " and a column of letterpress recording habits of tho species. Like many other foolish nocturnal moths, it is fascinated by lights. Members of the species quiver around a brilliant lamp in countless numbers. On the verandah of Mr. Hudson's house at Karori, Wellington, he attracted as many as a hundred individuals during two or three hours. It is by far the commonest insect that fell to his sugar, members of the species jostling one another to taste the sweets.

In his collecting days Mr. Hudson went out at dusk among plants from whose flowers moths sip nectar. The most suitable for his purpose were the veronicas, the white rata, the red rata, the scabious and the ragwort. He carried a lantern fastened to a strap around his neck or waist. Both his hands were fre.e to catch moths. When the flowers failed him he resorted to sugaring. He mixed" black treacle and rum in a tin. About sunset ho spread the mixture with a brush on treetrunks, palings or other objects that could be examined conveniently with a lantern after dark.'On some nights sugared trees swarmed with the commoner species of Noetuidae, a family to which the New Zealand army-worm belongs. On other nights few were attracted. In addition to its liking for treacle and rum, the army-worm moth swarms in bewildering profusion on all sorts of attractive flowers, crowding out rarer and more aristocratic species of moths.

During the day members of the specieß may be seen at rest. Their colours then protect them from observation, particularly if thev are partly concealed among grass. They are un"usually quick in taking to the wing. They may elude .pursuit during flight by making a sudden stop. Their season as perfect moths seems to be a long one, from September until May. They rear two broods every season. Most of them pass the winter wrapped up in the inertia of the chrysalis stage of life, but a few perfect moths may be seen on mild evenings in the middle of winter.

It may have been the same species that appalled agriculturists about 66 years ago. Caterpillars then marched through North Island districts in regiments, battalions and armies, devouring -crops" and leaving fields' as if no seed had been sown. To this day entomological text-books quote a telegram sent to New Zealand journals about that time, announcing that morning and evening trains between Waverley and Nukumaru on their way to Wanganui were brought to a standstill by countless thousands of caterpillars on the rails, which had to be swept and sanded before the trains could continue. Caterpillars completely threshed heavy crops of oats at Dunsandel, North Canterbury. A Dunsandel farmer watched them -march out of one man's paddock and cross the road to another man's paddock. Hastening to warn the man threatened, they put on the road 1600 sheep, which trampled countless caterpillars to deaths The road was black with them. When the warm weather came they caused a horrible smell.

The notorious American army-worm, Cirphis unipuncta, the caterpillar of a far-flung moth, present in New Zealand, is less troublesome here than in America, Hawaii and Australia. Members of the great armies mobilised by the American army-worm have a retiring disposition, but when their numbers increase so largely that food is scarce, or from sonic other cause, they become and migrate in thousands, stuffing themselves with plant food, as they go.

Australia's Bugong moth, Agrotis infusa, sometimes flies on board vessels far out in the Tasman Sea. It has been reported from lnvercargill, and probably is present in other parts of New Zealand, but is not plentiful here. This is fortunate, as, by its numbers, it sometimes is troublesome in Victoria and in Now South Wales. A relative, Agrotis ypsilon, whose caterpillars are called cut-worms, is more plentiful in New Zealand. Cut-worms do heavy damage by feeding on roots. This .species is almost cosmopolitan, occurring in New Zealand, Australia, China, India, Africa, Europe, North America and South America. In New Zealand, at this season, cut-worm caterpillars have advanced through their chrysalis stage. The perfect moths should be on the wing now. They should be much in evidence until April, paving evening visits to flowers. They are brown, their bodies are ringed with black, and their expanded wings measure 2in.

Massed movements of caterpillars still excite surprise among entomologists'. Major R. W. G. Hingston, in a recent book on instinct and intelligence, wrote: "I have never observed a migration of caterpillars, but we know that they advance with undeviating force. Imagine an army'of these crawling ravages eighty-five miles broad and thirty miles deep. They meet with a gully. It does not deflect them. Myriads fall in, choke it to the top with their dead bodies, and those that follow climb over the dead. Any that happen to halt or hesitate are submerged by the army that pours over them from behind. How ridiculous it sounds to speak of a railway train brought to a halt by a horde of caterpillars, yet such a thing happened in New Zealand. By crushing them in thousands the wheels became so greasy that the engine could no longer grip the rails. All were marchiug across the track, driven like locusts, butterflies, and dragonflies, by a blind, inflexible force." ,

An American entomologist, Mr. R. E. Snodgrass, wrote of another species of caterpillar, called web-worm, after studying it closely: " We are hopelessly above any intimate -understanding of a caterpillar's mind. Consequently, we aro loath to credit it with having any mind at all. It has a brain, a long nerve-cord and nerves that branch to all its parts and regulate its actions, in the same way as ours are governed; but a caterpillar's acts are attributed by us to what we call instinct, a word we can pronounce better than we can define. A brief outline of a web-worm's life illustrates how all its acts are primed to follow one another in unvarying sequence and to always operate at the proper time and place. Evory impulse is prearranged, predestined in the egg, as each individual goes through all the acts of its life in the same rotation." ' '