This may be one of the easiest features to add to your habitat, and a highly impactful one! Rocks and brush create shelter, nesting sites, and foraging opportunities for small mammals, birds, reptiles, and amphibians.
From the Xerces Society: Why do rocks, well, rock so much as shelter? Rocks are thick and sturdy, so they keep conditions beneath them relatively stable, even during more extreme weather. At high noon on a dry day, the space beneath a rock pile is shaded, cool, and damp. During a rainstorm, bugs huddling in the gaps in a stone wall are likely to stay safe and dry.
Even on normal days, rocks give invertebrates a useful way to control their body temperature. We humans can stay at more or less the same temperature all the time, but bugs cool down and heat up depending on their environment. Rocks hold on to heat particularly well, so a stone that’s been in sunlight all day will stay warm for quite a while after the sun has fallen low in the sky. I often spot some of my favorite jumping spiders seeking out warm rocks in the late afternoon or early evening.
Because they are unlikely to move or break down, many bugs prefer rocks for long-term shelter, too. For example, many types of beneficial beetles, like rove beetles, ladybug beetles, and firefly beetles, like to use cracks and crevices under rocks to stay safe over the winter. Bugs that build their own structures to live in and/or raise their offspring, like mud dauber wasps and some spiders–both excellent at natural pest control–love to use rocks as an anchor.
These piles need not be huge to be effective (although, the bigger the better). Start with some larger rocks or logs, and add progressively smaller ones on top. Make sure there are some open spaces between the pieces. For an added bonus, top off the pile with loose brush, pine boughs, or even discarded pieces from your Christmas tree. That’s it!
Learn more:
How to build a habitat pile (YouTube)