Munge Dweevil

The Munge Dweevil is an enemy in Pikmin 2. Like other types of Dweevil, this creature is commonly seen carrying enemy corpses and treasures. When agitated by attacks, it will release a cloud of gas that will poison all nearby Pikmin, excluding White Pikmin and Bulbmin. This suitably makes White Pikmin or Bulbmin the best choice in battle, as they are immune to poisoning. Alternatively, as Purple Pikmin can stun any common Dweevil with a 100% chance, they will defeat one easily. However, one should note that the Munge Dweevil has considerably more health than its relatives.

In Pikmin 4, due to the changed color of the poison hazard, they are replaced by the differently colored but functionally identical Venom Dweevil, though it lacks the Munge Dweevil's increased health.

Behavior
Munge Dweevils scurry about randomly and take no note of the presence of any leader or Pikmin if left undisturbed. When provoked, one will attempt to defend itself by releasing poisonous gas below it. This poison will scatter all attacking Pikmin, and eventually kill them if they are not whistled back to a leader. Munge Dweevils are frail creatures (though less frail than all other common Dweevils) and will die somewhat quickly if attacked by even a few Pikmin, or by the punches from a leader.

When a treasure or a corpse of another creature is nearby, a Munge Dweevil will lift it up onto its head and carry it, making it impossible for Pikmin to collect until it is broken free. When a Dweevil has an item in its possession, it will stay at rest, crouching down, appearing as if it is only the item, until it is approached by a leader or Pikmin, at which point it will stand up and run away.

Pikmin
It's safest to attack with White Pikmin or, if available, Bulbmin, as they are immune to their gas attack. Swarming them with either of these is a reasonable strategy that guarantees the safety of your Pikmin. A faster, if slightly riskier strategy, is to use Purple Pikmin; they are guaranteed to stun Dweevils with their pound, and a direct stomp to their head will do massive damage.

Swarming it with a large group of Pikmin regardless of type will also quickly kill it. Just be prepared to whistle, as the creature may still get an attack off before it dies.

Leaders
Simply punch the Dweevil to death. Both leaders are completely immune to poison, even without upgrades, meaning that the creature poses zero danger to them. Munge Dweevils, however, do have the most health out of the common Dweevil species, meaning that it may take a while without the Rocket Fist.

Using the Napsack to lay down near any Dweevil species will potentially make them pick up the sleeping leader, humorously allowing them to "ride" the Dweevil. When you are ready to kill it, just press to kick its head and stun it. Then, just punch it to death. This works for any small Dweevil.

Trivia

 * Strangely, the Munge Dweevil has 200 more health than other Dweevils, having 350 in total compared to the other Dweevils' 150 health.