` This block-quote comes from an article I was reading, in Nature News as I recall, which I thought was quite fascinating. Stanislav Gorb and team at the Max Planck Institute were studying pieces of glass on which zebra tarantulas were treading, when they unexpectedly discovered tiny remnants of solidified silk!
The observations are exciting because they reveal an attachment mechanism not seen in any other species of arachnid, says the team. And the finding may prompt a rethink of the evolution of spider silk.` In other words, it is thought that the ancestor of all spiders could have spun silk from its feet to help it stick to surfaces while climbing. As time went on, one pair of legs would have become useless for walking, though still functional for secreting silk. These became the familiar spinnerets, which small, web-weaving spiders use so often!
The researchers suggest that initially all spiders had the ability to secrete silk from their feet, but lost the skill because they no longer needed it.
Silk is usually produced by an organ called the spinneret, which is located on the lower abdomen. Gorb thinks that spinnerets may have evolved from leg appendages. "The finding that silk is directly coming from the feet supports this hypothesis," he says.
For now it is impossible to know whether foot silk pre-dates web spinning, or whether this type of tarantula evolved it separately. An examination of the genetics of the silk production should help to sort that out.
` Since silk is such an expensive secretion, the silk glands of the feet would have become a waste of protein for smaller spiders which do not need them for traction. Therefore, these glands were lost while larger spiders - which may not be able to crawl over slippery leaves and such without them - found them to be worth keeping.
` If an animal's legs becoming something other than legs sounds like a strange idea to you, be assured that this is not some unsupported, oddball idea that some crazy biologist thought up! For example, the mouthparts and antennae of various arthropods (a group which includes spiders, insects and crustaceans) are already known to be modified versions of legs! The spinnerets would be just one more example.
` However, the idea that spinnerets themselves are legs is not much more than a hypothesis for now until further research has been conducted. For example, it could instead be true that copies of silk glands sprouted up on the feet of a species of tarantula, which proved to be useful when climbing.