Encyclopedic version of How to Defeat a Red Bulborb
The red bulborb will be asleep at the beginning of each day. The bulborb will wake up if Olimar or a pikmin comes in contact with it. An awoken bulborb will wander within a large area around it, usually made obvious by gates, rocks and other such things. The red bulborb will wander towards the largest group of pikmin in this area, and use its sole attack on them (biting). In the event there are no pikmin in this area, it will head for Olimar. In the event Olimar is not in this area, it will return to the exact position it was originally sleeping in, examine the nearby area briefly, than fall asleep again. The red bulborbs biting will put any pikmin that come in the way of its large mouth into its mouth, where they will die in a few seconds. Killing the bulborb before those few seconds pass will save the pikmin inside. The bulborb performs a large dive as it bites, allowing an even larger group of pikmin to be eaten, but the bulborb will take a few more seconds to regain balance upon doing this. When a large amount of pikmin are attacking the bulborb at once, the bulborb will continuously flinch, demobilizing it for a time, before it eventually shakes, removing the pikmin from it. Only a small amount of the pikmin shaken off will loose their buds/flowers, and they will all proceed to attack the bulborbs feet upon getting up. If enough pikmin are placed on a sleeping bulborb, it will die before it gets a chance to shake.
NOTE: A lot of this information, especially pertaining to its behaviour, is simply from memory, and I've never tested any of this out, though it seems to be true. This is less of "How to defeat a red bulborb" than it is "red bulborb behaviour". I also didn't edit this much, so of course it has errors, but it is just an example.