By TheStreet Staff What Are Spiders (SPDRs)?Standard & Poor’s Depositary Receipts are known as spiders, or SPDRs. Managed by State Street Global Advisors, they represent an exchange-traded fund (ETF) made up of shares of a market sector or index. SPY, which is commonly used interchangeably with the term SPDR, is the most actively traded ETF in the stock market in terms of volume. SPY is made up of all of the companies in the S&P 500 Index, and because it tracks the S&P 500, many investors consider it to be a key component of their overall portfolio. Not only does SPY track the price performanc…