I like the unexpected use of the theme (every grapple point i.e. "life" expiring the moment the frog swings away, forcing players to figure out a sequence on the fly (no pun intended).
Took me a while to really figure out how it worked. imo I don't think the player should have to hold the mouse button to stay grappled onto a fly because there seems to be a lot of forward planning that the player needs to take into account based on how the flies are arranged and the potential strain of a finger perpetually held on the left click doesn't help matters. That and the game speed is too fast, meaning that I fall too quickly after jumping in and usually end up rapid-clicking in a panic anyway.
As it stands, holding the left click also seems temperamental in that even if I hold it down after the frog falls into range of a fly, it still snaps off and falls off the screen. I dunno if it's because my frog is carrying too much momentum as they swing, but if I were able to influence how much momentum I can exert while swinging with its tongue on a fly, I could feel more like it was my fault. I didn't get to play that far, but maybe have a spider web background that the flies are stuck on to communicate this more clearly (and that could pave the way for possible hazards later!)