From the Super Mario Wiki
Squigs are purple, pig-like enemies that are a stronger version of Squiglets. They are leaders for Squiglets which means that this causes Squiglet Armies to appear. Their first and so far only appearance is in the game Super Paper Mario. They have twice as much HP as Squiglets and unlike their weaker counterparts, Squigs can also spit rocks at Mario and his allies giving 10 points if the rock is destroyed. The rocks act the same to that of an Octorok's rock in the Zelda series. They appear in the Flipside Pit of 100 Trials in rooms 3, 7, and 8, and also in Chapter 1. They also assist Squogs in the fact that Squigs are in Chapter 7. They are known as Squog Armies.
If the player has Carrie, a pixl found in Fort Francis, they can do the best experience trick which gives the player lots of points if they time their jumps right on the rocks that the Squig spits out. As shown by this video of Youtube click here (This doesn't work without Carrie since the Squig will not always shoot a rock after a few jumps, even when the player tries to jump 11 times, the Squig will still stop shooting rocks).
Their name comes from the word "squirt" (small) or "square" and the word "pig".
Names in other languages