![]() ![]() In these cited studies, the influence of the added weight on the vertical position of the hub was analysed. One approach to increase the force acting on the spider is to glue small weights onto its abdomen (Mayer 1952 Vollrath and Köhler 1996 Herberstein and Heiling 1999 Coslovsky and Zschokke 2009). Previous experiments and observations on web building under altered gravity in the same direction as gravitational forces act for vertical webs) are increased or decreased during web building. However, to really understand the influence of gravity on web building, it is necessary to conduct experiments in which the forces acting roughly parallel to the web plane (i.e. Another striking vertical asymmetry is the orientation of the spider whilst waiting on the hub for prey to be intercepted by the web: with very few exceptions, spiders face downwards when waiting on the hub, which is also considered to be an adaptation to prey capture behaviour (Maciejewski 2010 Nakata and Zschokke 2010 Zschokke and Nakata 2010).Īs outlined above, gravity does play an important role in prey capture and web structure, and therefore, we can expect that gravity is also important during web building. ![]() Empirical and theoretical studies suggest that this asymmetry is mainly an adaptation to the spider’s prey capture behaviour and that it reflects the spider’s ability to run downwards faster than upwards (Masters and Moffat 1983 ap Rhisiart and Vollrath 1994 Maciejewski 2010 Zschokke and Nakata 2010). Mayer 1952 Witt and Reed 1965 ap Rhisiart and Vollrath 1994). Probably the most obvious asymmetry in orb webs is the hub position: in most orb webs, the hub is positioned in such a way that the capture area below the hub is larger than the capture area above the hub (e.g. Gravity is probably the reason for the sexual size dimorphism in some spider species (Moya-Laraño and Foellmer 2016), and last but not least, gravity influences the prey capture behaviour of spiders building vertical orb webs (ap Rhisiart and Vollrath 1994 Herberstein and Heiling 1999 Coslovsky and Zschokke 2009), which in turn affects the structure of these orb webs, resulting in vertical asymmetries in many different ways (Mayer 1952 Eberhard 2014 Zschokke and Nakata 2015). 1999), it is an important cue for honey bees whilst dancing on the honeycomb (von Frisch 1967), and it causes elephants to walk around hills rather than across them (Wall et al. Among many others, gravity induces the directed growth of roots and stem in plants (Chen et al. Gravity influences many organisms in a wide variety of ways. We conclude that in the absence of gravity, the direction of light can serve as an orientation guide for spiders during web building and when waiting for prey on the hub. In addition, spiders showed a random orientation when the lights were off but faced away from the lights when they were on. Closer analysis revealed that webs built when the lights were on were more asymmetric (with the hub near the lights) than webs built when the lights were off. We found that most, but not all, webs built in zero gravity were indeed quite symmetric. As these asymmetries are considered to be linked to gravity, we expected the spiders experiencing no gravity to build symmetric webs and to show a random orientation when sitting on the hub. Under natural conditions, Trichonephila spiders build asymmetric webs with the hub near the upper edge of the web, and they always orient themselves downwards when sitting on the hub whilst waiting for prey. During that time, the spiders and their webs were photographed every 5 min. Here, we describe the results of such an experiment where two juvenile Trichonephila clavipes (L.) (Araneae, Nephilidae) spiders were observed over a 2-month period in zero gravity and two control spiders under otherwise identical conditions on Earth. Probably the best approach to study the relevance of gravity on organisms is to bring them to the International Space Station. Gravity is very important for many organisms, including web-building spiders. ![]()
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