First things first. Civilians? We’re dead. We’re all dead. The biggest danger isn’t:

Sure, some people will get trampled to death by deer. Some will die to predators. But not many. Humans are pretty good at fighting tigers. You can shoot them, trap them, or burn their habitat to the ground.

No, where we die:

There are about 6 trillion bees on earth. That’s enough to sting every human 1000 times. What shape do you think you’d be in after 1000 beestings?

There are 100 trillion of these (ants). In fact, the ants probably outweigh the humans. They could literally drown us all in our beds as we slept. Not to mention:

or:

or, the all-time human-killer:

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So what happens?

Anyone asleep in their beds when the war starts is dead. They’d get bitten to death by rats, stung to death by bees, or drowned in a literal flood of ants.

The only people who survive the first attack are our armed forces, the ones stationed on ships. Maybe there are some survivors from the big cities, where there aren’t so many animals. But only the ones near the coast, who can get out to sea.

The sea isn’t safe either, not with the fact that sea life outnumbers land life. But if you can get to one of these:

you have a chance. I doubt even a coordinated effort from the fish could sink these.

But then what? We starve to death. Maybe with the firepower of one fleet you could carpet-bomb enough of some island to purge it entirely of animal life. But that island isn’t going to have much in the way of food on it afterwards.

But that’s humanity’s best chance.

Carpet-bomb some place like Hawaii until you’re sure not even the insects have survived. Then bring in some plants. We could make it, stranded on an island in the Pacific, thousands of miles from the rest of the world.

But I doubt it.