Well, I agree with the others. You may have been out of practice since you haven't been on for a while. You have to creep up on the beetles, careful not to scare them. If you are on your own island, what I like to do is dig holes with a shovel in front of all the palm trees. When I spot a beetle, I creep up in front of the hole ahead of the tree and once I walk in front of the hole, I swing my net and get the bug every time. When I'm on an island with other players, I prefer not to do this method as they dislike the holes and may walk past the bugs, scaring them and making them fly away. Also, silver nets are nets that have a bigger catch radius, meaning that you don't have to aim that much when you catch a bug on a tree. You can obtain silver nets by opening the Museum Shop, and donating 30 species of bugs to the museum. Here's an example of the trees.
T = Tree
BT = Beetle on Tree
H = Hole
P = Player
BT
H
P