Tuatara: Volume 23, Issue 2, July 1978
Studies on Populations of the Tunnel Web Spider Porrhothele Antipodiana — Part I: Characteristic Features and Seasonal Changes
Studies on Populations of the Tunnel Web Spider Porrhothele Antipodiana
Part I: Characteristic Features and Seasonal Changes
From studies on several populations of this New Zealand Mygalomorph spider the following characteristics emerged: (i) age structures showed marked seasonal variation, (ii) sampling for density indicated the spider is most successful in open habitats, (iii) migratory activity is a feature of many members of these populations, and dispersal rates of up to 100 metres/year are possible, (iv) over the summer months, a substantial change in numbers of mature spiders was noted in many populations. This was regarded as being due to the activities of Pompilid wasps.
Characteristics and Life Cycle of Porrhothele Antipodiana
P. antipodiana is a large, hairy mygalomorph spider of the family Dipluridae. It commonly grows to 30 mm in body length and is readily identifiable by its orange-brown cephalothorax, and a coating of long black hairs on its legs and abdomen. It spins a tubular or tunnel web which connects to a flat sheet web used for prey capture. The tunnel in which the spider shelters may be under a log or rock; in a crevice on a bank; in the hollow of a tree; and sometimes the spider may take up residence in or on buildings, a feature which often brings it to the notice of urban dwellers.
Published material on the ecology and behaviour of the spider includes two articles by this author (1973, 1975) and also the discussion of New Zealand mygalomorphs in the book by the Forsters (1973). The distribution, feeding patterns, postures, and behavioural repertoire have been described in these articles. A little is known of the spider's reproductive behaviour and of its movements about the page 68 habitat. Very little seems to be known of the population dynamics of this — or indeed of any other New Zealand mygalomorph — this article is an attempt to rectify the situation.
Information on the spider's life history has been presented in the chart below. The findings of the Forsters have been arranged side by side with information derived from the present study.
|Forster and Forster, 1973||Present survey|
|Egg-sac constructed in early to mid-summer.||Egg-sac constructed in late October to mid-December.|
|Eggs number 200-300.||Eggs number 100-300.|
|Spiderlings hatch in 30 days.||Young emerge from egg-sac when 2-3 mm in body length.|
|Most young leave parental web in February, body length 4 mm. Young disperse up to 1.5 m from parental web.|
|Spiders reach maturity in 2-3 years.||Spiders grow to 12 mm body length by end of year one. Females mature by end of year two when body length of up to 20 mm is reached.|
|Spider can live to at least 6 years of age.||Spider of 30 mm body length must be at least 5 years old.|
The information from the two sources is quite comparable, and the differences in the egg-sac construction time, for instance, could well be due to climatic differences between the Wellington region and the lower South Island. In most of the populations studied, very few mature males were found. The ratio of mature males to mature females was often as great as 1 : 100, and very commonly around the 1 : 50 mark. The population figures quoted in this articles will therefore refer mainly to female spiders.