I was discussing this offline the other day. The sweet spot that really needs to be hit is something that is both creepy and threatening.
This renders lots of larger creatures, like bears, as somewhat off-model. I think if you want a mammal - other than bats, which are worth a second go - something like hyenas, which have the benefit of laughing and coming off as somewhat mangy, might be your best bet. Hyenas also have the benefit of living throughout much of Africa.
I suggested that things that swarm are pretty much overplayed, specifically as far as bugs are concerned. Maggots are a strong thought insofar as they're legitimately repulsive, but I'm not sure they seem immediately dangerous enough.
That said, bees and the like are worth considering, though also being territory somewhat owned by The Wicker Man remake. They do have the benefit of flying. I think wasps or hornets would be closer to the mark than bees, especially with bees being endangered.
I like Indyfan82's general idea of tying the creatures into the quest more, though as for locusts specifically, I'm not terribly keen on them going back to the Biblical well. Locusts would also, arguably, be re-trodding the agricultural devastation theme of Temple of Doom.
They've lost their chance on piranhas, I fear, having been to the Amazon in the most recent installment and not following through on that. That said, there's some indication that a scene with Mutt being bitten by a piranha was filmed and cut, so possibly the general idea of threatening fish is something they'd like to revisit.
Certainly, having the creature scene in the water would be offering a twist on it. Jellyfish is a compelling thought; so too are eels. Or anything in the cephalopod family, which, like most mammals, offers the possibility of working with a larger creepy creature. Possibly also some really threatening crustaceans.