This is your interpretation of Mark 16:15. St. Francis had his, and his is the plain reading of it. I guess, "all creatures" does not mean "all creatures" to the Sola Scriptura superstitionists.
Do you preach the Gospel to flies?
Not consciously. Preaching the Gospel is living it, and as we live among the animals of all kinds we preach to all of them in the language they understand. This is the central theme you as a Calvinist don't understand: The Word is a body of Christ, not a book, so preaching the Word is behavior, not speech. This is why St. Francis spirituality drives you nuts. Luther, and especially Calvin never understood the Gospel, and the Gospel continues puzzling you, and Christian behavior contuinues puzzling you.
For the record, preaching to animals is not a Catholic dogma. One can be a good obedient Catholic and never pet a dog. The reason I underscore it is because your puzzlement over it highlights the impoverished state of Reformed spirituality.
Prayer of St. Francis
Lord, make me an instrument of your peace,
Where there is hatred, let me sow love;
where there is injury, pardon;
where there is doubt, faith;
where there is despair, hope;
where there is darkness, light;
where there is sadness, joy;
O Divine Master, grant that I may not so much seek to be consoled as to console;
to be understood as to understand;
to be loved as to love.
For it is in giving that we receive;
it is in pardoning that we are pardoned;
and it is in dying that we are born to eternal life.
