A comparative study of the biology of the Giant wetas Deinacrida heteracantha and D. fallai (Orthoptera : Henicidae) from New Zealand

The complete life cycle of Deinacrida fallai Salmon and D. heteracantha White takes a little over two years. In neither species is the cycle tied very rigidly to the seasons. About four months is required for the development of the egg; nymphal stages last 12 to 14 months in D. fallai, and about 18 months in D. heteracantha; adult females of D. fallai live about eight months and males about 11 months; adult females of D. heteracantha live about four and a half months and males about seven months. Nymphs of D. heteracantha have a marked winter diapause. This is much less pronounced in D. fallai. D. fallai become adult in the late autumn, and D. heteracantha in the spring. The sex ratio is uneven with a preponderance of females to males. Maturation of the gonads is more rapid in D. heteracantha than in D. fallai. Mating occurs through most of the year, normally during daylight. Four different body positions have been observed, vertical turning of the male under the female being most common. This position has not previously been recorded in the Gryllacridoidea. Only one spermatophore is produced at a time, but up to six or eight may be produced in a day. Deinacrida possesses four of the seven hypothetical primitive characters for genetalic structure and copulatory behaviour suggested by Alexander & Otte (1967). Oviposition occurs at night and eggs are laid individually in the soil, with a mean of 27 laid at any one time. They are laid over a three months period in D. fallai, and a two months period in D. heteracantha. Nine nymphal instars are passed through in D. fallai, and 10 in D. heteracantha. After the first four instars D. heteracantha is heavier than D. fallai. Before oviposition the female body weight increases up to 200% in D. heteracantha, and up to 100% in D. fallai. Regeneration of portions of appendages occurs in both species. Reduplication may also occur. The process of ecdysis is similar to that in other species of Orthoptera. The exuvia is colourless. It is eaten in D. fallai, and discarded in D. heteracantha. Variations in colour of different instars are recorded. The mortality rate in both species is very high. Favourite habitats for wetas are on kanuka, pohutukawaand fan palms. Both species are primarily vegetarian, but in captivity cannibalism occurs. Both species are nocturnal. Harriers and moreporks are predators of the wetas. A number of potential predators are listed. Protective behaviour consists of burrowing head first into soft earth, or hiding under loose bark or inside holes in rotten wood. In both species males are more aggressive than females, and can display sexual aggression. Two distinctive types of sound producing mechanisms are present in both sexes and are a generic characteristic. Apart from Deinacrida, abdominal stridulation has not been recorded amongst Orthoptera. This is the first detailed study of the biology of species belonging to the Henicidae.