Years ago I found this white silken cocoon-looking thing in the bottom of my bluebird box and had no idea what it was. As I was removing it from the box, I accidentally tore the edge of it and all of these small yellow balls spilled out. Come to find out they are spider eggs!
Spiders, like insects, start their lives as eggs. Spiders wrap their eggs in silk, which they produce in their bodies and then shoot out through faucet-like spigots on the backside of their bodies called spinnerets. All spiders produce silk, but not all of them build a web, as many are active hunters who stalk their prey rather than try to catch it in a silken trap.