From the Super Mario Wiki
In New Super Mario Bros. Wii, they appear only in World 7-6 and in New Super Mario Bros. U, they appear only in Soda Jungle level Flight of the Para-Beetles, along with its smaller relatives. They act as platforms for Mario and company to jump on to get across the level. Despite being three times the size of a normal Para-Beetle, the Heavy Para-Beetle cannot stand the weight of any character and begins to descend when stepped on, unlike their smaller cousins, who fly higher when stepped on. Like normal Para-Beetles, the Heavy Para-Beetles can be defeated only by running into it with a Starman, and only in New Super Mario Bros. Wii, Yoshi can eat an iceball and spit it at them to freeze them then the player can either ground pound or jump under them to defeat them. They can not hurt the character while he is standing on its shell, but its exposed head and underside can hurt the character. Like the other Para-Beetles, if the player jumps on a certain amount, 1-Ups fall down to the player, or each player depending on the amount of people playing.