Wood mulch piles have some very real dangers associated with them, ranging in seriousness from bothersome to devastating. As a general rule, you should keep your children and pets away from them as they are not safe playthings. Above and beyond this rule, however, you need to care for mulch piles to keep your plant and home life safe.
When mulch sits in piles -- even just a few feet tall -- for a long period of time, the centers of the piles become oxygen-deprived. As this process progresses, toxic gases form in pockets. When you lay down this mulch around your plants, the toxins leach into the soil, killing your plants within a few days. You can avoid this fate, by smelling the mulch before you lay it on the ground. If it smells like rotten eggs or vinegar rather than organic fertile soil, you may have a problem, and you shouldn't let the mulch anywhere near your plants. Once you discover the problem, you can fix it by laying the mulch down in a thin layer on a tarp or pavement for a few days and watering it to leach out the toxins.
Wood mulch piles are flammable, even more so than a pile of wood. The centers of the piles can get very hot and, combined with a hot, dry summer, can spontaneously combust. Most catch fire due to smoldering cigarette butts, so if you have a pile of mulch, keep smokers away from it at all costs. The fire usually starts and smolders in the center of the pile for a while, eventually erupting into flames and burning anything nearby. To avoid disaster, store piles away from your home or any other structures.
If you have a problem with ants or earwigs invading your home, it could be due to the pile of mulch in your backyard. Ants and earwigs love to build nests in these piles and can multiply quickly. For a smaller chance of invasion, keep the piles away from your house, and when you spread the mulch, do so in thin layers to prevent further nest-building activities.
For the best mulch results, distribute it to its respective landscaping and garden locations within a few days of delivery. If you must keep it in a pile for a longer period of time, however, you should not neglect to first take a few safety precautions. Split a large pile up into smaller, more manageable piles and place them in the coolest location you can find. Every few days, take a shovel and turn the mulch, so that the center receives oxygen. Spread the piles as soon as you can, in a layer no taller than 2 or 3 inches.