Maybe it's the eighth leg...

In the book Spidersilk, there were a lot of elements that worked together to help Mark successfully take down his enemies and restore his amazing quality of life. One of the biggest contributions to this was the Spiders that were protecting Mark. Most of us have a fear of spiders because they can be deadly, but are also mysterious and hard to predict. However, in many different cultures the Spider was seen as a protector. Many Native American tribes used to pass down stories of the wisdom the Spider protected to the point that the Spider was often referred to as a grandmother. Islam also presents the spider as a protector who helps weave strength into life. Protection from Mark's enemies was not the only thing the Spiders may have helped Mark with. In fact, his prosperity in finances and friendships might have been because of these mysterious eight legged creatures.

If you're interesting in knowing more about the symbolism behind spiders check out this cool page:

http://www.whats-your-sign.com/spider-symbol-meaning.html