A researcher in Britain says she's settled a long-running debate over how tarantula spiders manage to climb walls and hang upside down - seemingly impossible tasks for the big, heavy arachnids.
Her study has confirmed that tarantulas can shoot sticky threads of silk from microscopic spigots on the bottom of their feet to prevent a potentially deadly tumble. Even a short fall that would not harm the average web-spinner would likely spell death for the hefty, fist-sized tarantula, a ground-dweller that can weigh as much as 50 grams.
Like many other spiders, tarantulas have silk-producing organs called spinnerets located on their abdomens. Rather than spinning webs, the giant land spiders use their silk to line or guard their underground burrows. They have also been known to build hammock-like structures for a cozy place to spend the day.
Scientists have long believed that tarantulas grabbed silk from the spinnerets to secure their grip on vertical climbs. But in recent years, experts have speculated that the sticky silk was actually coming from the spiders' feet. Biologist Claire Rind of the University of Newcastle decided to take a closer look. Examining naturally-shed tarantula exoskeletons with a high-powered electron microscope, Rind was able to detect tiny silk-producing spigots protruding from the hairs covering the spiders' eight furry feet. In experiments with live spiders climbing the walls of a glass terrarium that was then tipped on its side, she also observed that the weight-conscious arachnids only produced safety silk from their feet when they felt themselves slipping.
The researcher says the tarantula's ability to spin silk from its feet suggests it could be an evolutionary link between the first silk-spinning spiders 386 million years ago and their modern web-making ancestors.
The University of Newcastle scientist made the same finding in three geographically remote species of tarantulas she studied - the Chilean Rose, the Indian ornamental, and the Mexican flame-kneed. Given the diversity of the three species, Rind believes it is likely that all tarantulas have the ability to shoot safety-silk from their feet.
The study will appear in the June edition of the Journal of Experimental Biology.
tarantula (n) 狼蛛; 毛蜘蛛
settle (v) 結束（爭論、爭端等）；解決（分歧、糾紛等）
spigot (n) 塞，栓
tumble (n) 跌倒；滾落；暴跌
spell (v) 招致，意味着（通常指壞事）
hefty (a) 大而重的
英國的研究可望解決為何毛蜘蛛能爬牆與倒掛的爭論(to climb walls and hang upside down)。對又大又重的毛蜘蛛來說，這些動作應該是不可能的任務(impossible tasks)。原來，毛蜘蛛的腳底有極微小的吐絲口(microscopic spigots)，可以射出具有黏性的蜘蛛絲(sticky threads of silk)。此來，毛蜘蛛可避免原本會致命的一摔(a potentially deadly tumble)。對其它蜘蛛同類來說，小小的一摔沒有什麼損害，但對於體型壯碩、拳頭大小(hefty, fist-sized)的毛蜘蛛來說，意味的卻可能是死亡(. . .would likely spell death for . . .)。
burrow (n) （動物的）洞穴，地道
vertical (a) 垂直的
exoskeleton (n)外骨骼; 外甲
terrarium (n) 小植物（玻璃）栽培盆；小動物（玻璃）飼養箱
跟其它蜘蛛一樣，吐絲器也會在毛蜘蛛的腹部找到(located on their abdomens)。但對主要在地面移動的毛蜘蛛來說，吐絲卻不是用來結網，而是用來補強與保衛他們的地下居穴(burrows)。毛蜘蛛也會利用蜘蛛絲來建構像是吊床一樣的結構(hammock-like structures)，好整以暇的待上一天。之前的研究就發現，毛蜘蛛會用腹部的吐絲器來輔助直向的爬動(vertical climbs)，但近年來研究人員開始還懷疑，其實毛蜘蛛是利用腳來吐絲的。研究人員用高倍數的電子顯微鏡(high-powered electron microscope)來觀察毛蜘蛛的外骨骼(exoskeletons)發現，在毛茸茸的八隻腳裡(furry feet)，可以看到微小但凸出的吐絲開口。在實驗中把毛蜘蛛放在傾斜的玻璃飼養箱(a glass terrarium)裡攀爬，對體重一向很敏感的毛蜘蛛(weight-conscious arachnids)如果感到抓不穩、打滑的情形(. . .felt themselves slipping)，就會從腳底吐出安全絲(safety silk)。
evolutionary (a) 進化的；演變的；逐漸發展的
ancestor (n) 祖先
ornamental (a) 裝飾性的；點綴的
diversity (n) 多樣性；多樣化
研究人員指出，這發現是對三億八千六百萬年前與近代會結網的蜘蛛的演化史上的一個連結(an evolutionary link)。此外，研究人員也相信，即使在地理上相差遙遠的(geographically remote species)毛蜘蛛品種，雖然品種間存在差異性(diversity)，都可能具有從腳底吐絲的能力(the ability to shoot safety-silk from their feet)。