Art. XXVI.—The Mole-cricket (Gryllotalpa vulgaris) in New Zealand.
[Read before the Wellington Philosophical Society, 25th July, 1888.]
It is generally believed that New Zealand has no native mole-cricket: this belief is probably correct—at any rate, its existence has yet to be proved; though it is stated, on the authority of Mr. Churton and Major Parry, that one species (Gryllotalpa africana) has been found here. This species has, however, a wide range, being found in South Africa, India, and Australia. It is probable that the specimens referred to were introduced from the last-mentioned country; and Professor Hutton, who compiled the “Catalogue of New Zealand Orthoptera” published by the Colonial Museum and Geological Survey Department in 1881, states that he has never seen New Zealand specimens.
I have on previous occasions had to bring under the notice of the society the occurrence of European butterflies and of the scaly lizard in this country, and pointed out that as cultivation extended, and the importation of plants increased, so the introduction and spread of noxious insects would increase, and their depredations become more serious.
The most recent addition of this kind is the English mole-cricket. Some years ago a specimen was brought to me by a son of the late Rev. Mr. Harvey, and I was assured that it had been captured in New Zealand. I, however, took little notice of the matter at that time, and neither saw nor heard anything of further specimens till a short time ago, when I observed some children with the two specimens I now exhibit. The youngsters stated that they had dug them out of a bank on the Tinakori Road, near the Botanical Gardens. Both specimens are immature, but undoubtedly belong to the European species.
In England and on the Continent—especially the latter—the mole-cricket is a terrible trouble, doing incalculable damage in the cornfields, pastures, and gardens. Germany and the south of France suffer most extensively, but the pest is gradually and surely working its way northwards, and is also common in many parts of England, especially in moist districts.
In Germany they have been known to destroy as much as one-fourth of the young corn-crop. They are also very fond of peas, beans, cabbage, and lettuce. Should they find their way into a kitchen-garden they will sometimes destroy whole beds of young plants in a single night. They burrow in the ground and eat the roots, so that the destruction is complete.
One species has of late years caused enormous damage amongst the pastures and sugar-cane plantations in the island of St. Vincent.
They live underground, are large and very powerful, and are said to be capable of propelling a 61b. weight on a smooth surface. Their fore feet are like those of a mole, and are peculiarly adapted for burrowing. During the day they remain in their burrows, along which they can move backwards or forwards with equal facility, being provided with two filaments at the end of the abdomen, which are used when a backward movement is desired.
These insects are probably familiar to some of you, and I have here specimens and drawings which may be examined, so that it is not necessary I should inflict on you a description of their personal appearance.
At the beginning of summer the female excavates, near her burrow, a cavity shaped somewhat like a lemonade-bottle, with a long neck, which is turned up and communicates with the surface and with her burrow. In this chamber she deposits some three or four hundred eggs. She then carefully seals up the entrance. In about a month or five weeks these eggs, which are about the size of small peas, hatch out, and the young at once commence to feed upon the tender roots of the surrounding plants.
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When first hatched they measure only from 1/12in. to ⅛in., and are destitute of wings, but when adult they measure nearly 2in., and have wings.
They pass the winter months in the earth, coming forth as spring advances. Their presence may be traced by the little mounds of earth like miniature molehills, and by the yellow withered patches which disfigure pastures and gardens.
I have now seen three specimens captured in New Zealand; it is therefore reasonable to suppose that they have, to some extent at least, established themselves here, and it is probable, in consequence of the rapid progress new pests
always make in this country, that in time, unless great care is taken, we may find the mole-crickets as troublesome as they are in Europe.
Luckily, there are numerous ways of getting rid of them, and nature helps considerably, for the mother herself frequently eats large numbers of her children. Their sense of smell is very acute, and it has been found a good plan to bury a dead crab in the ground infested by them, or pour water with a little oil or turpentine down their burrows, when those not killed will at once vacate.
The mole-cricket, though feeding principally upon vegetation, is really omnivorous, and will take raw beef, grubs, &c., with zest. It has been stated that they are really useful because they do this, but the best authorities give them an unqualified condemnation.
Like their relations, the field-crickets, they are very war-like, and have cannibalistic tendencies, for when an enemy has been vanquished he is sure to be eaten.
Addendum.—Since this paper was read the author has been informed that Mr. Robinson, of Makara, near Wellington, is familiar with the mole cricket, but does not think it has increased in his district during the last two or three years.