Gaaaaaah Iains!! Western green mambas are extremely venomous! Good job you used the pipe. I'm usually in favour of trying not to kill things that are dodgy, just run away (eg enormous spiders) but mambas are another thing altogether. Although the green ones are normally fairly timid, if cornered or they feel threatened, they'll strike. Inevitably fatal...
Grubs are probably quite nutritious and tasty. As long as something is well-cooked, it shouldn't do one any harm.