Crab

Crabs are decapod crustaceans of the infraorder Brachyura, which are generally covered with a thick exoskeleton and come armed with a pair of pincers. In the Crash universe, they also make a few appearances as generic enemies.

Crash Bandicoot
Crabs are the first enemies encountered in this game - and, by extension, the entire series. They appear mainly on "N. Sanity Beach" although a single one can be found in "Jungle Rollers". They do not directly attack Crash, instead simply walking from side to side while blindly snapping their pincers. They easily fall to a jump or spin attack.

Crash Bandicoot 2: Cortex Strikes Back
A crab makes a cameo appearance in the less-than-100% completion ending, passing by as Coco wonders what happened to Doctor Neo Cortex and his Cortex Vortex.

Crash Bandicoot: The Wrath of Cortex
Crabs make a reappearance in the level "Crash and Burn", where they randomly scuttle from left to right shadowboxing at Crash. They can first be found at the beginning of the level just when crossing the dock after riding the Turtle there. When Crash gets near them, they start punching the air with their pincers.

Crash Twinsanity
Crabs reappear as generic enemies. They appear on "N. Sanity Beach" and "Jungle Bungle" where they block Crash by his every movement - unusual, as real-world crabs typically do not live in jungles. Their appearance seems to be a deliberate throwback to the first game in the series. However, these crabs wear shells, implying that they are hermit crabs and, therefore, not the same crabs that Crash Bandicoot fought in Crash Bandicoot. In this game they can dig underground to pop out of the sand to ambush Crash.

Crash Landed
Crabs was going to be one of the enemies in the game. But instead only appeared in the DS demo version for Crash Landed since the game got cancelled.

Personality
As for having three different species, they all have different personalities, some holding no malice, and some with the urge to fight.

Crash 1 and 2: These ones have been shown to hold no malice towards visitors or locals, but for an unknown reason it constantly snaps its claws, and accidentally harms anything that hits it, and as an example of it holding no malice towards anyone, the Crab in the ending of Crash 2 simply walked by Crash and Coco without attacking them or running into them.

Crash Bandicoot: The Wrath of Cortex: These Crabs seem to have the urge to guard their perimeter, by shadowboxing from left to right, trying to block out anything coming their way.

Crash Twinsanity: These ones have a much more aggressive personality, by attacking anything that comes by and ambushing it by popping out of the sand to attack it, and ones in the Jungle seem to try to block creatures out of their perimeter like the previous Crab.

Locations
These Crabs have bred in different places, but almost never off of "N. Sanity Island", as demonstrated in Crash Bandicoot: The Wrath of Cortex, where the first Crab off of "N. Sanity Island" is seen on the Volcanic Island in "Crash and Burn", but of a different species than the ones seen in the first two games. Hermit Crabs have been seen living on "N. Sanity Beach" in Twinsanity, and oddly enough, in the Jungle, but not too far from the Beach, making only three appearances there.

Types
As of appearing in several games, these have different species with different movements:
 * The Original species randomly walks from left to right snapping its claws in the level "N. Sanity Beach" as a basic generic enemy.
 * The same species in Crash 2 walks to its right then takes a curve and continues walking to its right.
 * In The Wrath of Cortex these ones too walk from left to right, but shadowboxing at Crash.
 * In Twinsanity, these Crabs walk entirely random, even walking over rocks and digging into the sand and popping out in random areas.
 * In Twinsanity's first level "Jungle Bungle", these Crabs follow Crash's movements from left to right trying to block him.

Trivia

 * The appearance of crabs as enemies in the Crash games appears to be a reference to the many famous crab enemies from Nintendo's rival Mario series, including Sidesteppers from Mario Bros. and Clawgrip from the true Super Mario Bros. 2.
 * This is one of the few enemies that pop up infinitely.
 * The crab was the first enemy ever to be introduced in the Crash games.