There is an important moral puzzle to solve, because this is an ongoing problem. To simplify the problem and push it to an extreme where the issue is easy to see, I am going to frame this as a trolley problem.
Imagine that there is a person in a room with two buttons. They are told that they have two minutes to decide which button to push. If they push the button on the left, a child will be spared from death, but some quantity of invertebrate animals will be killed. If they push the button on the right, a quantity of invertebrate animals will be spared but the child will be killed. If they push neither button, both the child and the invertebrate animals will be killed. Accept for the hypothesis that the person believes this to be the truth.
Now we zoom out, and get to you. Turns out, you are watching this scenario through a hidden camera. In front of you is a single button. You are told that if you push this button the person you are watching in the room with two buttons will be killed and the child will be spared. If you do nothing, then you will simply not interfere with their choice.
Under what circumstances would you push the button? Does it matter what number of invertebrate animals' lives are on the line?
For me, it does not matter what number of invertebrate animals' lives are on the line. As soon as I see the person reaching for the button to kill the child, I will hit my kill button to kill them and spare the child. If they reach for the button to kill the invertebrates, great! Both they and the child get to live. I do not think this is a matter of personal taste, I believe it is a moral rule. That I would be wrong to do otherwise. So wrong, in fact, that if there were a third room with a person watching me and deciding whether to push the button to kill me and the original subject, that I would argue the third person has a moral obligation to kill both me and the original subject if the original subject reaches for the button to kill the child and I do not stop them.
Try this with any combination of number and type of invertebrate animal, and my answer will stay the same. A billion cockroaches? A trillion squid? A Graham's Number ants? No hesitation.
If there was no child's life on the line, if it were simply spare the invertebrates or kill them? I would not press a kill button to prevent someone from killing the invertebrates. I would be sad if they chose to kill the large number of invertebrates for no reason, but not morally justified in killing them. There is no number of invertebrate animals which would make me feel justified in killing the person to save the invertebrates.
Why am I picking on invertebrates here? Because their brains are relatively small and simple. So small and simple that I argue that, wherever the minimum line for 'experiencing meaningful suffering' or 'moral relevance' is, they are below it. I'm down to discuss whether, and to what degree great apes or dolphins or elephants deserve moral consideration. I have empirical reasons from examining their brains and their behaviors to believe that these creatures may indeed be moral agents. Cockroaches? Absolutely not within the bounds of reasonable argument.
Examine their behaviors. Do they exhibit behaviors we could reasonably interpret as forming empathic social bonds or reciprocal social contracts? No.
Look at their nervous systems. Do they have complex networks of neurons devoted to social interaction and compassion for self and others? No. Ability to experience sensory stimuli and interpret it as aversive is insufficient. They don't have the capacity to have emotional valence on top of those aversive stimuli, they don't have emotions, they don't care for themselves or others. They don't make choices with moral agency, deciding between doing good things or bad things. They are emotionless robots obeying genetically hardcoded instructions with only a little simple learning. They do not build a complex worldview and rich episodic memories. They do not ascribe rich personal meaning to events and experience desire for possible future outcomes. They are not little humans or even puppies, scaled down to tiny sizy and simpler brains. They are categorically a different thing which lacks all attributes of experience that give moral worth to a creature. No large number of zeros adds up to anything but zero. Cockroaches are not 0.000001 of a human, they are pure zero. With animals, there is gray area, a gradient of sorts, and we can talk about where to draw what lines. Invertebrates aren't on the scale.
So when people talk about 'Charitable Cause Prioritization', and their discussion includes protecting invertebrates and trades this off against protecting humans, I think they are mistaken. I don't think there is a valid tradeoff there.
So what's the problem? Why don't I just let the invertebrate-lovers go do their thing, while I do mine? The problem is that those arguing for the invertebrate cause as an issue of moral importance have brought bad arguments to the table. And then these arguments were not rejected. I'm fine with people bringing in new possible arguments about novel moral issues to consider. I'm not fine with failing to reject those potential moral issues when the arguments turn out to be flawed.
In practice, these issues do compete. When we are hosting a global conference about doing good, and we choose who to include as speaker and attendees, we are making choices. When we choose what posts to allow on our internet forums, we are making choices. When we decide what organizations to include in a list of 'affiliated charities', we are making choices. These all trade off against alternatives, including the alternative of not including them and thus not diluting a list of organizations pursuing valid causes with organizations pursuing incorrect ones.
I am asking for the community to make a stand and draw a line. While there are people dying of hunger, of currently preventable diseases, or of medical problems we could potentially find cures for (e.g. senescence, cancer), then we should firmly state that people matter morally in a way that invertebrate animals do not. Until all the human problems of sufficient threshold to be moral issues, such as involuntary death, have been completely solved, we should stop validating expending resources or attention on the welfare of invertebrates.
Welcome to the Forum!
This post falls into a pretty common Internet failure mode, which is so ubiquitous outside of this forum that it's easy to not realise that any mistake has even been made - after all, everyone talks like this. Specifically, you don't seem to consider whether your argument would convince someone who genuinely believes these views. I am only going to agree with your answer to your trolley problem if I am already convinced invertebrates have no moral value...and in that case, I don't need this post to convince me that invertebrate welfare is counterproductive. There isn't any argument for why someone who does not currently agree with you should change their mind.
It is worth considering what specific reasons people who care about invertebrate reasoning have, and trying to answer those views directly. This requires putting yourself in their shoes and trying to understand why they might consider invertebrates to have actual moral worth.
"So what's the problem? Why don't I just let the invertebrate-lovers go do their thing, while I do mine? The problem is that those arguing for the invertebrate cause as an issue of moral importance have brought bad arguments to the table."
This is much more promising, and I'd like to see actual discussion of what these arguments are, and why they're bad.
wonderfully welcoming comment, @Jay Bailey! :)