there will often be the problem of extraneous sounds getting in the way (planes, roads, HVACs) but if the area is particularly quiet, any low self-noise, sensitive mic placed very close to a tiny sound will yield something interesting.
A simple piezo disc stuck inside an anthill (depending on your local ants, check that they wonât try to eat you in retaliation) can do wonders.You can also stick the piezo to a larger object (or plant) that will become a walking/roaming etc area for those little insect footsteps.
Last year i discovered that when clamping a piezo to a tree branch, you are somehow listening to the environment âthroughâ the tree, as the leaves act as membranes and their vibrations are conducted down the wood fibres to the contact mic (it is quite obvious but i never thought about that before hearing it). I suspect this might be more interesting with quality contact mics with a fuller bandwidth.
tl;dr: For tiny sounds, 1/if in a silent environment, putting an appropriate mic very close to the source works. 2/ contact mics may also work.