Ants, no question.

"Fun" fact: The biomass of all the ants in the world is greater than the biomass of all warm blooded (endothermic) animals combined.

Absolutely ants. The sheer volume of every ant in the world working together would be horrifying

There are an estimated twenty quadrillion (20,000,000,000,000,000) ants in the world. They could wipe out all terrestrial life on earth if they wanted.

Easily ants. Google ant swarm animal. But not right before bed. There's a few insects that are evolved specifically to fight ants but everything else is food to them.

Ants easily, there are literally so fucking many. Like there are some singular species of ants that I think could did it alone

The antlions

Ants just because of quantity. There's estimates out there and it's just ridiculous amounts of ants.

You know those timelapse youtube videos where you watch ants eating a small fruit within a couple of days? Imagine that, but with it happening a lot faster with so many ants covering lions that you wouldn't be able to see them.

Another vote for ants, although that's partly because I'm a fan of the film Phase IV in which all ant species suddenly start cooperating with each other against humans.

Humans. Because the lions would be overwhelmed in short order after which the ants would kill each other off.

There are roughly 39,000 lions left in the world, none of which eat insects.

There are roughly 20 quadrillion ants on earth, a significant portion of which will eat live mammals, and almost all of which will kill any ant not from their own colony.