If the pet store was right down the street from Wal Mart, you could have suggested walking over there and back for your crickets while she was shopping at Wal Mart so she didn't have to make another stop. At 16, you should certainly be trusted to walk a few blocks or so by yourself to buy some crickets. After five hours in Wal Mart, one can't blame either of you for being a bit off, but the screaming does seem somewhat out of bounds. Your Mom must have gone over the edge for some better reason, even considering spending five hours in Wal Mart as being a good reason in itself. How did YOU behave during this episode? Are you responsible for your own obligations such as school and homework? Do you help with chores without being nagged about it or resenting it? It will help your relationship if you are able to act like a responsible, reasonable adult yourself, even if your parents sometimes don't. It's a hard row for everyone.
Your parents love you, even if they may not seem to at times, and you do love them, whether you are always aware of it or not. They may "suck" at times, and perhaps you also "suck" in their view, at times, but the unequivocal love connection is always there. It just sometimes gets obscured by daily frustrations and life stresses.
You aren't alone, believe me.
Advice is like kissing: it costs nothing and it's a pleasant thing to do. (George Bernard Shaw)