Happy Ha-Ha Bugs are bugs that tickle people. They appear in the episode Woozy Walden.
We first see them in the book that Wubbzy and Daisy were reading about the different bugs Walden was going to show.
The other time we see them is them Tickling Wubbzy first making him laugh hysterically and making him do things with his tail. Then they attacked Daisy.
When Dr. Flooey comes in the Happy Ha-Ha Bugs was still Tickling the two and they were on the floor and then retreated after they heard him and they still acted like they enjoyed their little tickle fight.
The final time we see them was when Wubbzy asked if they forgot to put away the Happy Ha-Ha bugs obviously they did and ended up tickling him again but this time they did it also to Dr. Flooey and Widget and it looked like they were stomping on them and that was the end of the episode.''
When they tickled Wubbzy and Daisy they apppear to attach themselves to their backs. Although before starts laughing if you pause the screen just right you can see his tail change itself just before and the duo will fear their tickling feet momentarily.
It is unknown what happened to the bugs afterwards but they maybe still doing their tickle attacks to Wubbzy and Daizy.