Skeletal animations tend to have some drawbacks. Aside from being one of the biggest drains to framerate, creating them is as complicated as modeling a 3D character. Once the skeleton is made, and the object skinned to it, creating the keyframes can be a bit daunting. Creating the animations isn't too hard, with a few tips.
0: doing things by the tens:
You only need to make a keyframe at specific intervals. I suggest every five to ten frames. (1,10,20,30,40)
1: Most things can be done a few bones at a time:
Head bobbing and tail wagging can be done after the major (walking) animation is done. This also goes for arm swinging.
2: ANIMATE ALL THE LEGS!:
Yes, do them in pairs. Each leg of a pair should have the same exact animation, but each pair should have a different animation. Front pair of legs should cycle forward while the back legs cycle back. Then just grab opposing (front_left, back_right) and drag them back two keyframes. Then take the keyframes that hang off and move them to the front. This offsets the leg animations.
3: Bugs are not that hard:
For 6-8 legged creatures, assign pairs of legs to a bone. Assign the front and rear left legs to a left bone, then the middle to a different left bone. For spiders, left legs 1&3 to one bone and 2&4 to another. Now just animate those bones like you're rowing a boat. Simple and creepy.
Of course, when you import them to a game engine, they can still get wrecked.
Remember to have the mesh and skeleton centered (world and object) properly to avoid some pitfalls.
If the characters need to be rotated, apply transforms and delete older versions of the export and import files (to be safe).
If it works, save the animations files before you break it.
Keep the hierarchy as much as you can when preparing the actual character for use in-game.
Keep calm, or find a punching bag.
