The total amount of suffering in the world is (maybe) far less now than it was a hundred years ago.
loss of wildlife populations vs factory farming.
World facing first mass extinction since the dinosaurs as wildlife populations plunge by 67 per cent in 50 years | The Independent
"wildlife populations plunge by 67 per cent in 50 years"
"They found that between 1970 and 2012, the average decline in population was 58 per cent. "
Depression is something that only happens in social animals, and factory farmed animals probably spend almost all their time in a negative state whereas wild animals are probably only negative most of the time.
Still if you do the numbers the devastation that humans are causing are reducing suffering in the wild.
Insect populations are another thing.. I don't think there's much data on insect populations now vs 100 years ago, and as you recognise they probably don't have the same level of mental anguish.
It's possible that even though they don't have the same "in your head" suffering, the "escape from the fire" suffering is much more intense than humans.
Humans can rationalise going to the dentists, having an injection or working out because they can see into the future and anticipate that it's going to be a good thing for their future self, animals that don't have our foresight ability might experience massively more distress.
just some thoughts..
Also there are shitloads of people working on human suffering, animal suffering is neglected and it's not clear that you can't do both or even that helping animals will make us friendlier and want to help humans more too, they're not mutually exclusive.
At a guess I think maybe 99.99999% of suffering on earth doesn't occur in humans.. this number is kinda pulled out of my arse though. If Brian is right it's far more, if insects can feel pain but it doesn't amount to suffering it's a fair bit less. then bacteria sperm and atoms and so on, it's a tough one.