This is a Sow Bug, a Terrestrial Isopod. These guys proliferate in dark, damp areas like worm bins. They munch on decaying matter alongside the Red Wigglers causing no harm inside the worm bin (in fact they help out with the composting process), however outside they can cause damage to your plants and garden.
Sow Bugs need constant moisture to survive and are primarily nocturnal so a moist dark worm bin is perfect.
Can you find the Sow bug in my bin?