I've read through all the posts here, and I'm well aware of balance issues on Cave and Jungle. I'm planning to lower the price to start up the generator in Cave stage, and I'm probably going to lower the chance of Trappers placing traps.
The Musca bug sucks, I thought I had fixed it in the past but it's still here. I will fix that soon.
I mean... Those changes will help, sure, but fail to address the major problems with those stages.
Flies are too fast to run from and difficult to hit, so the player MUST turbo out a decent automatic weapon in the first five rounds or be dead. Right now it's impossible due to the massive cost to even access the weapons shop, and even then victory or death is completely dependent on one, maybe two rolls on the shop to get the Uzi/Auto Pistol. Maggots are too small and hard-to-hit, they cannot be simply shot in the middle of a wave as very few weapons can reliably hit such a small target, regardless of the player's ability to aim, and they're extremely difficult to spot. Making them at least twice as big is a given, but... maybe an audio cue? Have them work more like poison arrows, slowing players down and using their current attack if too many latch on?
The problem with Bear Traps isn't that there's too many of them, it's that they end up places where the player can't deal with them (on the ground beneath the trees, on platform edges too far to shoot from below and too close to climb up) and hitting one is a practically guaranteed grapple from pursuing hostiles. So, they either need tighter restrictions on where they can be placed (Perhaps only placing when the player can see them, so if there are traps in bad spots it's kind of the player's fault) or they need to be less punishing to hit (Cripple speed, maybe can't jump, but no knockdown). Simply reducing the rate will still result in !bullshit!, just less often.