From the Comox Valley Echo, Tuesday 3 September 2013, Ask a Pro
Question: Will my composter work better in the sun?
Answer: Surprisingly, we have found that the composters do better in the shade. If they are in the sun they tend to dry out too fast and need to be frequently watered to keep the worms and microbes damp and alive. The heat from decomposition comes from the thermophilic (heat-loving) bacteria, not the sun. These bacteria are just as enthusiastic in the shade. Worms are happiest in a temperature between 15 and 25 C. And worms like it dark. If your best option for the location of your bin has to be a sunny spot, just make sure that it stays damp. Keep the lid on to slow evaporation. However, sometimes on rainy days I leave the lids off for lazy-girl watering. The worms are grateful. And happy worms make salubrious compost!