LOL…I haven’t heard anything about flies and other insects having souls…but “praying mantis” may be working on it…
All living things have souls. Every last one. The Church has taught this for centuries. However not all living things have an immortal/rational soul.
Only a person can reflect upon God, think about God, love God. Animals though endowed with a kind of intelligence do not have an intelligence that can reflect upon divine realities. Only human beings ask themselves “why?” “how?” and search for Truth in the most transcendental sense of the word. Dolphins, chimpanzees, etc while all displaying sometimes highly complex (for animals) behaviors and even having the ability for some degree of abstraction, cannot reach these immaterial human heights. And how is it that we can? Because there is something “immaterial” within us, something that is spiritual and thus immortal.
Also only human beings have a moral life that seeks to be in accord with the divine will. It would be pretty silly if we put dogs on trial for being naked in public wouldn’t it? After all, if they are spiritual animals too, have they no shame? How do they know that other dogs aren’t going to see them exposed! Also, wouldn’t it be absurd if we thought ill of a lion for killing a zebra and eating it? But notice how to kill a human being, including the unborn, is nothing more than murder! Animals do not partake in this, they only live as they were created to be.
Notice how we speak of being the best, holiest, person that we can be…hopefully a saint! but that we never say this of animals. That’s because animals already are doing all that they can and are meant to do as God created them, unlike us, they cannot transcend their particular natural condition…where as we can be divinized and we can partake in the Eucharist!
Have you ever heard of a dog, cat, llama, shark, grizzly bear, sparrow, being canonized as a saint? No, and you never will. Animals will not partake of the beatific vision.
Remember how Christ told his disciples that God cares for the birds and the flowers…but how much more immensely God loves them. This was Jesus recognizing that human beings have an exalted dignity and that God loves them in a particular and exalted way.