Scanning Electron Micrographs Of Draglines Of Nephila Clavata Spiders And The Research Of The Relation Between Weights And Mechanical Properties Of These Draglines

We collected draglines secreted by 15 Nephila clavata Spiders when they falling down instantly,then we used the SEM to observe these draglines of single branch, take pictures, and used the Smileview software to deal with the pictures,measured and Stat the diameters of these single branch draglines.The results indicate that with the increase of the weights,the diameters of single branch draglines have increased corresponsively,the average diameter exhibit the obvious positive correlativity with the weights.The result also indicates the draglines of Nephila clavata spiders have presented the variety of fibre structures,the number of the single branches is uncertainty, and the diameters length of the single branches have many differences.The draglines which we observed,we found that they are not only made up of two similar shapely single branches,but also made up of two branches(one thick, one thin),three branches(three similar shapely branches;two thick and one thin;one thick and two thin),four branches,even eight branches at best,and even in the same dragline, the diameter of the single branch have many differences.The diameter of single branch is the important guide line of the tensile mechanical properties of the dragline,the bigger the cross section area of the single branch, the weight it can bearing is more.The result of the experiment indicates when the spiders falling down instantly,they can adjust the bearing weights of draglines by control the diameters of the single branches for protecting their safeness.We used single-fibre electronic tensile instrument to test fifteen single branches of draglines of different weights spiders,we had got the Force-Displacement curves, combine with the diameters of single branches,turn it to Stress-Strain curves,from the two curves,we can find out, as the elongate of draglines,the load has nearly linear ascend,the initial elastic modulus is very big,and bended when the stain has got to 2.5%,the curve had turned,modulus had got down instantly,even to zero,then the stress and modulus had got up again.From the Stress-Strain curves, we can get the result,which shows that the single branches secreted by the same spider nearly have the same strain at the proportional limit,and there have a great differences between the stress at the proportional limit,the breaking strength and the strain at breaking point.The stress at the proportional limit of single branch of different spiders has no correlativity with the weight;the strain at the proportional limit of single branch of different spiders has no correlativity with the weight;also,the strain at breaking point have no relations with the weight.These are not reflect the increasing trend with the weight.But the breaking strength of the draglines has increased with the weight increased; reflecting a great correlation with the weight. When the spiders falling down,they need to secrete the draglines which can only bear themselves' weights,the changes of the draglines' mechanical properties have no significance for the safeness of the spiders.To analyze the data of the weight and the breaking strength of the spiders,we found that the single branch can bear 1.35 times of the spider's weight.Therefore, when spiders falling down instantly,the draglines which are made up of several single branches can insure the safeness of the spiders themselves.But when spiders falling down instantly,the speed is much quicker than this experiment,so it is complex to compare the relation between the bearing weight and the spider's weight, and need to further research.