Robinson, Michael H., and Barbara Robinson. Ecology and Behavior of the Giant Wood Spider Nephila maculata (Fabricius) in New Guinea. Smithsonian Contributions to Zoology, number 149, 76 pages, 30 figures, 11 tables, 1973.-Investigations of the seasonal, reproductive, and population ecology of Nephila maculata are reported in detail. In an investigation of feeding ecology over a one-year period, the discarded remains of the prey caught by a sample population of ten adult female spiders were collected daily. These remains were identified (where possible) and the accumulated weekly discards from each spider were dried and weighed. Data from this study are analyzed, tabulated, and compared with the catches from insect traps located in the study area. The study included an investigation of web structure, frequency of web renewal, and the number of kleptoparasites associated with Nephila maculata. Studies of behavior included courtship, mating, predatory behavior, and responses to predators, sunlight, and rainfall. Courtship behavior included a complex pattern of silk deposition by the male on the female, here reported for the first time for the Araneida. The predatory behavior of N. maculaia is analyzed in terms of behavior units and behavior sequences and is compared with that of other Nephila species, related species, and that of other araneids studied by the authors. The phenological aspects of the study are stressed and discussed. OFFICIAL PUBLICATION DATE is handstamged jji a limited .number of initial copies and is recorded in the Institution's annual report, Sm^tnsonian Year. SI PRESS NUMBER 4779. SERIES COVER DESICN: The coral Montastrea cavemosa (Linnaeus). Library of Congress Cataloging in Publication Data Robinson, Michael H. Ecology and behavior of the giant wood spider Nephila maculata (Fabricius) in New Guinea.

The stabilimentum of orb web spiders is a structure for which several functions, both mechanical and defensive, have been suggested. Argiope argentata (Fabricius) builds a stabilimentum in the form of a white diagonal cross. Analysis of over 2500 webs of this species shows that the perfect cross is seldom built and nearly two thirds of the webs contain no stabilimentum at all. Experiments with wild birds as predators show that they can use stabilimentum-like models in prey location. From these data, and a review of the defensive adaptations of orb web spiders, it is argued that the A. argentata stabilimentum is not an anti-predator device. The evidence for a mechanical function is reviewed and discussed. It is suggested that the stabilimentum provides the spider with a means of making a final adjustment to the mechanical state of the web when this is necessary.

The prey caught by mature female Argiope argentata was censused over a period of one year. Ten webs (when available) were examined five times each day, at two‐hourly intervals, between 09.00 and 17.00 hours. The prey‐animals seen in the webs were classified into orders and lower taxa, where possible. The results of this study are described and discussed.

The response of five species of crabs to simulated predator attack was examined. Two terrestrial species autotomized their chelipeds after the chelae were firmly attached to the predator. Selection for attack autotomy is balanced by selection for retention of the cheliped whenever the cheliped is important in social or maintenance functions.

The araneid spider Pasilobus sp., common in the Morobe District, New Guinea, builds its web at night close to bushes and small trees. The more‐or‐less horizontal web has a triangular frame that is divided into halves by a midline thread running from the apical angle to bisect the base. From the midline thread hang 4–11 pairs of widely spaced spanning threads; these are the only adhesive elements in the web. The spanning threads are viscid for only part of their length and are strongly attached to the web only at their junction with the midline thread. The outer end of each spanning thread forms an easily ruptured, low‐shear joint with the lateral frame thread of the web. When a flying insect strikes a spanning thread, the low‐shear joint breaks and the thread drops below the web, leaving the insect tethered to the midline. The insect may continue to fly, on the tether, or may spin down to motionlessness. The spider rushes to the midline thread end of the tether, hauls up the spanning thread and then bites the insect. Experimental investigations of the low‐shear joints and the adhesiveness and elasticity of the spanning thread are described and the results analysed. The web‐building behaviour of Palilobus differs in several ways from that of most araneids and is described and compared with that of Gasteracantha and other species. The possible evolutionary origins of the Pasilobus web are outlined.