In Touch with nature

New Zealand Herald, Volume LXXIII, Issue 22540, 3 October 1936, Page 10 (Supplement)

In Touch with nature

By R. A. FALLA, M.A.

Specially Written for the New Zealand Herald

A CORRESPONDENT has sent a clipping taken from one of the best known magazines of popular science in the world, published in America. It includes a paragraph about the "vegetable caterpillar" of New Zealand, part of which is as follows: "The origin of the vegetable caterpillar, if wo are to credit local accounts, seems to have some connection with the rata tree, a parasite of somewhat singular characteristics. The rata seed borne through the air takes root in the fork of its host tree, gradually crushing the life out of it by sending out encircling feelers and finally assuming the shape of a legitimate forest tree. It is under the rata tree that tho vegetable caterpillar is found. Its presence is detected by a sharp tail-like spike extending above the surface of the soil. It is 'said that the caterpillar feeds upon the rata foliage and ultimately drops to the foot of the tree, where it bores itself into the earth. But the rata spores have 1 entered via its breathing tube, and soon eat it up all save the outer shell. The viscera, upon investigation will be found to be entirely displaced by a chalky fungoid substance. The only semblance to the original larva is the outer skin which maintains aJI the outlines of its former inhabitant." Legends of this kind aro common in the nature lore of every country and they are never entirely overtaken and killed by the less popular literature of scientific fact. Perhaps some day a pub-lic-spirited scientist may forsake his

laboratory and set out on an itinerant mission to bushmen seeking to put them right about how the rata tree begins and what a vegetable caterpillar really is; he will find it no easy matter to gain converts. The bushman, however, is not to be singled out for blame in this matter, for during the years that tho life history of tho vegetable caterpillar was being investigated and worked out even scientists fell into pitfalls of error and remained in them for a long time. Long after it was recognised that this

The Vegetable Caterpillar

LEGEND AND SCIENTIFIC FACT

strange object was a fungus that parasited a caterpillar, tho victim, or "host" as it is euphemistically termed in scientific literature, was thought to be tlu larva of our largest moth, the 1 ghost or puriri moth; and'this in spite of the facts that the vegetable cater- i pillar occurs where the ghost moth is unknown, and also that tho former is always found underground, while the latter lives in the heart-wood of trees. Tho fungus concerned is of the genus Cordyceps, which is not confined to New Zealand although four of the five species found hero are not known elsewhere. Tho most conspicuous is Cordyceps Robertsii. As mentioned above the identity of the host was long in doubt. The late Mr. A. Phil pott, then working in Southland, was the first in New Zealand to suggest that it might bo the largo subterranean caterpillar of a moth of the genus Porina, one of the several "grass-grubs." Other in- | vestigators obtained confirmatory evidence, and finally, Mr. G. V. Hudson, placed the matter beyond all doubt by identifying the host in the North Island as a common species cf Porina moth. Dr. G. H. Cunningham in his valuable studies of the New Zealand fungi baa; outlined tho process of the infection of the caterpillar host by the parasite. From tho ripe head of a fullgrown fungus spores are borne by wind or insects and scattered on the ground among leaves or logs. A spore, on coming in contact with tho body of a caterpillar, germinates and produces a germtube which penetrates the cuticle and body-wall. A further branching development of the germ-tube enables the germ-cells of the fungus to reach every part of the caterpillar's body in the blood stream, in which manner the fungus rapidly spreads and kills the ] host. What is apparently a dead caterpillar is now in reality living tissue of a fungus, which, after a period of rest, sends a fructifying stalk above the ground to discharge in duo course its ripe spores. Species of Cordyceps with similar habits are found in most parts of the world and they have in some countries attracted the attention of the native people. It is said that in Tibet a "grass worm" of this kind is credited with . rare medicinal virtues. Cordyceps Robertsii is known to the Maoris as awheto, by whom it was not eaten but used in tho tattooing process. According to tho late Mr. Elsdon Best, the "body" or vegetable portion of the fungus was burned and pulverised, and the powder so obtained mixed with water to form a black paste. This pigment was considered not sufficiently black for use in facial tattoo, but good enough for other parts of the body. After the pattern had been marked, and incised with a sharp implement, a second implement which had been dipped in the pigment was applied to the incision. There appears to be no foundation for the belief that the vegetable caterpillar is always found beneath the rata tree; it has been recorded just as frequently in areas where no rata is found growing. The life history of the rata fc itself seems fated to the same distor--3 tion in popular account as that of the . .vegetable caterpillar. The quoted ac- , count from the American magazine is substantially correct in describing the * origin of the rata. The northern rata 1 usually commences life as an epiphyte - from a seed lodged in a fork of the ; host, and its growth thereafter is . downward toward the ground. Through confusion with other species of rata, which are climbers, the northern rata is often thought to be a climbing parasite whereas the exact reverse is the case.