Grab a tool like ILSpy or JetBrains dot peek
Then open Rimworlds main library
<path-to-the-rim>\RimWorldWin64_Data\Managed\Assembly-CSharp.dll
and search for 'insect'. You'll find a class named
ThinkNode_ChancePerHour_InsectDigChance
To change the default behavior you have patch the method inside.
See https://harmony.pardeike.net/articles/patching.html
If you're able to understand code (in c#) you can do it
Then open Rimworlds main library
<path-to-the-rim>\RimWorldWin64_Data\Managed\Assembly-CSharp.dll
and search for 'insect'. You'll find a class named
ThinkNode_ChancePerHour_InsectDigChance
To change the default behavior you have patch the method inside.
See https://harmony.pardeike.net/articles/patching.html
If you're able to understand code (in c#) you can do it