Best insulation system below a wood floor exposed to nature
You can use foam boards (XPS or EPS). Cut these to the appropriate width, place in the joist bays, glue/screw as needed and fill in the gaps with canned spray foam. Those are fairly resistant to exposure within a crawlspace.

Consider sealing off access into the crawlspace if possible. You'll never keep all the insects out, but covering access holes with chicken wire or mesh will help keep raccoon or other scratching/digging animals out.