Password  Level  
2512      Jungle1   
2563      Cheese1   
1655      Medical1   
4216      Desert1   
5226      Tools  
1245      Egypt  
2643      Hell  
4136      Treehut  
5413      Garden  
3266      Snow  
2255      Constyrd  
3631      Pirate  
1451      Fruit  
3644      Alien  
4333      Circuit  
6316      Medieval  
*Note: Default level, no code required. 

Each worm corresponds to a certain number in the password. Here is the Key:

Skeletal worm = 1 
Pink worm     = 2 
Dynamite      = 3 
Red worm      = 4 
Banana bomb   = 5 
Blue worm     = 6  (drowning)