Why do nocturnal orb-web spiders (Araneidae) search for light?

The nocturnal orb-web spider Larinioides sclopetarius lives near water and frequently builds webs on bridges. In Vienna, Austria, this species is particularly abundant along the artificially lit handrails of a footbridge. Fewer individuals placed their webs on structurally identical but unlit handrails of the same footbridge. A census of the potential prey available to the spiders and the actual prey captured in the webs revealed that insect activity was significantly greater and consequently webs captured significantly more prey in the lit habitat compared to the unlit habitat. A laboratory experiment showed that adult female spiders actively choose artificially lit sites for web construction. Furthermore, this behaviour appears to be genetically predetermined rather than learned, as laboratory-reared individuals which had previously never foraged in artificial light exhibited the same preference. This orb-web spider seems to have evolved a foraging behaviour that exploits the attraction of insects to artificial lights. Received: 8 June 1998 / Received in revised form: 18 January 1999 / Accepted: 19 January 1999     

Association networks in spider monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>)

We use two novel techniques to analyze association patterns in a group of wild spider monkeys (Ateles geoffroyi) studied continuously for 8 years. Permutation tests identified association rates higher or lower than chance expectation, indicating active processes of companionship and avoidance as opposed to passive aggregation. Network graphs represented individual adults as nodes and their association rates as weighted edges. Strength and eigenvector centrality (a measure of how strongly linked an individual is to other strongly linked individuals) were used to quantify the particular role of individuals in determining the network's structure. Female–female dyads showed higher association rates than any other type of dyad, but permutation tests revealed that these associations cannot be distinguished from random aggregation. Females formed tightly linked clusters that were stable over time, with the exception of immigrant females who showed little association with any adult in the group. Eigenvector centrality was higher for females than for males. Adult males were associated mostly among them, and although their strength of association with others was lower than that of females, their association rates revealed a process of active companionship. Female–male bonds were weaker than those between same-sex pairs, with the exception of those involving young male adults, who by virtue of their strong connections both with female and male adults, appear as temporary brokers between the female and male clusters of the network. This analytical framework can serve to develop a more complete explanation of social structure in species with high levels of fission–fusion dynamics. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and R. James)     

Prey detection without successful capture affects spider’s orb-web building behaviour

Animals obtain information from past foraging experience to adjust their foraging activity according to their environment. The ability of spiders to obtain information from unsuccessful predation experiences was investigated by examining the effects on web building, a significant foraging investment, of prey detection without successful capture in the orb-web spider Cyclosa octotuberculata. Four treatments were employed: (1) successful capture and feeding: one syrphid fly was allowed to be captured and consumed by the spider on the web; (2) single prey-item detection: a syrphid fly was placed on the web to lure the spider, but was removed before capture; (3) five prey-item detection: above prey-item detection stimulus was given five times; and, (4) control: neither prey nor feeding on the web. While control spiders decreased the total thread length and capture area of their webs, prey-item detection spiders in both conditions increased them, indicating that the spider obtained information from unsuccessful predation experience to adjust their foraging investment. The fed spiders exhibited a significantly greater increase than the prey-detection-only spiders, suggesting that prey detection alone and prey detection with consumption had different informational effects. Total thread length did not differ between single and five prey-item detection spiders, but distance between two adjacent sticky spirals increased only in the former spiders, possibly because five times unsuccessful predations prevented spiders to reduce web stickiness. It suggests that the spider changed web morphology according to the number of prey detection.     

Homing in the wolf spider Lycosa tarantula (Araneae, Lycosidae): the role of active locomotion and visual landmarks

Previous studies on the homing of the wolf spider Lycosa tarantula have shown that it is carried out by path integration. Animals using this mechanism must measure the distance walked and the angles turned. This study aims to understand if wolf spider L. tarantula is able to estimate the walked distance in an outward path. As this information is more likely obtained by proprioceptive mechanisms, active or passive displacements have been performed. An active locomotion was found essential to estimate distances. During passive locomotion, spiders searched for their burrows near the release point while when displaced actively the inbound journey was longer than the outbound one. The possible use of visual landmarks near the burrow was also tested as a cue to complete the inbound journey. Our results did not show that L. tarantula used these visual landmarks to find the burrow. L. tarantula seems to use only proprioceptive information obtained during the outbound path to estimate the distance traveled.