Wurmple, like its other Bug NU bretherens, suffers from a staggeringly low set of moveset choices, making the listed attacks the most useful Wurmple can learn. Bug Bite is your main STAB attack, and can take down Ralts and, to an extent, Caterpie because of Wurmple's higher Attacking power.
56 Speed allows you to outspeed a neutral-natured, 0 Speed Turtwig for a Bug Bite attack, although most 0 Speed variants invest heavily in defenses, so Wurmple will have a harder time dealing damage to it regardless. Attack is maximized to give Wurmple the most powerful damage output, while the rest of the EVs are dumped into Defense to give Wurmple the upper hand against Caterpie, Silcoon, Cascoon and Jigglypuff.
Wurmple is a slower, but more powerful version of Caterpie. If you prefer higher defenses and Attack power over raw Speed, Wurmple makes a better candidate for your team than Caterpie. However, like most other Bug-types, Pidgey, Zubat, Torchic and Cyndaquil all cause big problems for Wurmple, as all pack super-effective hits, and are resistant to Bug attacks. Piplup is a very good teammate for Wurmple, as it resists Fire, and can pack a STAB Surf for Cyndaquil and other Fire attacks, and can learn Ice Beam to take care of Flying-types. Squirtle is also an alternative to Piplup if you are willing to sacrifice sheer attacking power for better defenses.
Zubat shuts down Wurmple entirely with a x4 resistance to Bug, and can take a Tackle while hitting Wurmple with a super-effective Heat Wave, Air Slash or Sludge Bomb. Cyndaquil and Charmander are also resistant to Bug, and can use Flamethrower to take down Wurmple. Pidgey and Starly are in the same category.
In UU, Gastly shuts down Wurmple entirely with a resistance to Bug, and immunity to Normal attacks. It can then proceed to attack with any neutral attack, and while it may not be a OHKO, Wurmple cannot do much to it in return. Even with a Choice Band, Wurmple's attack don't usually do much in UU, and even neutral attacks are usually enough to leave a considerable dent in Wurmple.
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