One of the biggest pests in any garden would have to be the caterpillar. One day your veggies look great, and the next they have been totally stripped!! The Cabbage White Butterfly is the most common cause after laying its eggs which develop into these pesky little chewers.
The best way to stop caterpillars is to stop the egg laying proccess in the first place, but this is very hard to achieve unless you are growning in a fully sealed off and protected area. One simple remedy is to throw a protective cover over your garden such as a light vegetable mesh. As long as it is very light (and lets the light through) your plants will push it up as they grow without affecting their growth at all. This won