Evolution beyond the orb web: the web of the araneid spider Pasilobus sp., its structure, operation and construction

Abstract

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.

The Natural History and Behavior of the Bolas Spider Mastophora Dizzydeani SP. n. (Araneidae)

“…(Robinson and Robinson 1975) Robinson and Robinson 1975). This movement is similar to and was probably derived from the pulling movements many araneids make with legs IV as they lay sticky spirals (Robinson and Robinson 1975, Eberhard in prep.).…”

“…C Both M. dizzydeani females and Pasilobus catch moths almost exclusively. This specialization in M. dizzydeani is probably due to the use of moth sex attract pheromone mimics (Eberhard 1977), and it is possible that the same may be true for Pasilobus (Robinson and Robinson 1975 (Forster and Forster 1973) and Taczanowskia (Eberhard in press) adopt the same daytime resting posture as that of Mastophora. In sum, the data suggest that the traditional groups of Cyrtarachneae (including Cyrtarachne, Pasilobus, Poecilopachys, and four other genera), Mastophoreae (including Mastophora, Dichrostichus, Cladomelea, and three other genera), and Celaenieae (including Celaenia and Taczanowskia) (Roewer 1942) should be placed together in the same section of the subfamily Araneinae. It is reasonable to ask why natural selection would favor such radical reduction in trapping webs in this group.…”

“…Hutchinson (1903) also noted that disturbed M. cornigera produced an unpleasant odor which came from a drop at the mouth. Robinson and Robinson (1975) suggested, on the basis of their study of Pasilobus and Clyne's work (1973) on Poecilopachys, that there is an evolutionary series starting with typical orb weavers and passing through Poecilopachys and then Pasilobus to the bolas spiders Mastophora, Dichrostichus, and Cladomelea. They established several links in web architecture and function between Poecilopachys and Pasilobus.…”

Molecular Phylogeny of Moth-Specialized Spider Sub-Family Cyrtarachninae, which Includes Bolas Spiders

“…Observations were made sporadically over several days, during which time the spider moved to a new location about 2 m above the ground in the leafy branches of a Citrus × limon. At the new site it was observed to construct a catch-web resembling the one illustrated in Robinson and Robinson (1975).…”

A revised and dated phylogeny of cobweb spiders (Araneae, Araneoidea, Theridiidae): A predatory Cretaceous lineage diversifying in the era of the ants (Hymenoptera, Formicidae)

“…842 (Stowe, 1986) [0], Parawixia bistriata (Rengger) (Fowler and 843 Diehl, 1978;Fowler and Gobbi, 1988) [0.13], Pasilobus sp. 844 (Robinson and Robinson, 1975) [0], Poecilopachys sp. (Stowe,845 1986) [0], Poltys laciniosusKeyserling (Smith, 2008) [0], Pycnacan-846 tha tribulus (Fabricius) (Dippenaar-Schoeman and Leroy, 1996) 847 [0], Scoloderus cordatus (Taczanowski) (Stowe, 1978) [0], Zygiella 848…”