Wurmple's evolution is not based on IVs, but instead an obscure mechanic called personality values. Personality values are 32-bit integers the game generates for Pokemon each time they are encountered. The rest is just a bunch of math.
Personality values are responsible for determining a number of things, including natures, genders, abilities and more. It is also responsible for Wurmple's evolution. It does this in different ways in each generation, so I'll assume you'll want the most up-to-date information from gen 6. In that case, the game will take the first two bytes of Wurmple's personality values (16 bits) and divides its decimal value by 10. The game will then calculate the remainder from the calculation; if this is less than 5, Wurmple will evolve into Silcoon. If it is equal to or greater than 5, it will evolve into Cascoon.
We can apply this to a real situation. For example, if a Wurmple had this set of personality values:
We'd take the first two bytes, indicated in bold, and divide their decimal value by 10. The decimal value, 51,852, has a remainder of 2 when divided by 10, therefore this particular Wurmple will evolve into Silcoon.