Verified against Pokémon Database and Bulbapedia, current as of the mainline Switch-era games (Scarlet/Violet, Legends: Arceus) plus Pokémon GO. Values are stable across generations for this line — no patch has changed how Wurmple splits since Generation III.
You caught a Wurmple, levelled it to 7, and watched it turn into a Cascoon instead of the Silcoon you wanted. Before you reset your save or start hunting for a “trick,” here’s the part that matters: the outcome was already decided the instant that specific Wurmple was generated, using a value the game never shows you and you were never able to influence. Soft-resetting and re-catching the exact same Wurmple won’t change it either — evolve it again and you get the same result every time[1].
The Personality Value: What Actually Decides Silcoon or Cascoon
Every Pokémon carries a hidden 32-bit personality value the moment it’s generated — the same underlying number that also quietly sets nature, gender, and (in older games) shininess odds. For Wurmple specifically, the game takes the last 16 bits of that value and runs one calculation: divide by 10 and keep the remainder. A remainder of 0–4 produces a Silcoon. A remainder of 5–9 produces a Cascoon[2].
That split isn’t something the developers documented in-game — it was reverse-engineered and confirmed through repeated community testing, including contributors who ruled out competing theories (which move you used first, what time of day it was in the mainline games) by testing them directly and getting the same Wurmple to evolve the same way every time regardless[2]. As a general guideline, treat the personality-value explanation as settled: it’s the only mechanism that has survived direct testing.
To see why that’s a genuinely unforgiving check, walk through the math on a single value. Say a given Wurmple’s personality value ends in the 16-bit segment 65,532. Divide that by 10 and the remainder is 2 — under 5, so that Wurmple becomes a Silcoon. Change nothing except the value itself to 65,535, and the remainder becomes 5 — now it’s a Cascoon[2]. There are 65,536 possible 16-bit values in that range, and roughly half land on each side of the 5 threshold, which is why the split behaves close to a coin flip in practice even though it’s really a fixed lookup, not a live roll made at evolution.
The practical result: the value is set the moment the specific Wurmple spawns, not when you throw the ball, not when you level it up, and not when you evolve it. Catching it later, using a Rare Candy instead of grinding, holding an item, or evolving it at a different time of day in the core series changes nothing[1].
What Doesn’t Decide It — Common Wurmple Myths, Busted
| Claimed factor | Does it work? | Why |
|---|---|---|
| Time of day (any game, including Legends: Arceus) | No | A claimed Legends: Arceus day/night rule doesn’t survive a source check — see below |
| Which move you used to weaken it | No | Directly tested and disproven; the split doesn’t read move history[2] |
| Holding an item while levelling | No | No item interacts with the personality-value check |
| The Wurmple’s nature or IVs | No | Nature is a different derivation of the same personality value — correlated in origin, not causally linked |
| Soft-resetting and re-evolving | No | The value is static per individual Wurmple; the same one always resolves the same way[1] |
This is the same category of “hidden, unchangeable value” mechanic we broke down for Combee’s gender-locked evolution — different trigger, same lesson: not every branch in this franchise is a choice, and treating an RNG wall as a puzzle to solve wastes real playtime.
The Legends: Arceus “Exception” You’ll See Claimed Online — and Why It Doesn’t Hold Up
Search around and you’ll find guides claiming Pokémon Legends: Arceus breaks the rule entirely — evolve a Hisuian Wurmple during the day and you get Silcoon, evolve it at night and you get Cascoon, giving players their first real control over the split[10]. It’s a clean, appealing story. It also doesn’t hold up against the two sources that would actually confirm it. Bulbapedia’s Wurmple page, which is otherwise thorough about documenting per-game exceptions to standard mechanics, describes the exact same personality-value split for Legends: Arceus as every other core-series game and lists no time-of-day carve-out anywhere[1]. A dedicated Legends: Arceus walkthrough covering the same evolution admits the outcome “seems completely random” and couldn’t confirm a reliable day/night pattern despite testing it[12].
Evolution in that game is manual either way (triggered from the party menu once Wurmple hits level 7, not automatic on level-up), so it’s easy to see how a player who happened to evolve a few Wurmple during the day and get Silcoon each time could walk away convinced they’d found a rule. Until someone publishes a large-sample test that actually holds up, treat the “you can control it in Arceus” claim as unverified rather than fact — the honest answer, backed by the sourcing that exists, is that no release has ever given players a confirmed way to pick Silcoon over Cascoon.
Pokémon GO doesn’t offer any workaround either — spending 12 Wurmple Candy still produces a random Silcoon or Cascoon with no way to bias the result, gender included, and you’ll need a second full evolution cycle (another 50 Candy from that specific line) to reach a final form[11].
Silcoon and Cascoon Are Statistically Identical — the Choice Doesn’t Matter Yet
Here’s the detail almost no guide mentions: whichever cocoon you land on, it doesn’t matter competitively until level 10. Silcoon and Cascoon run the exact same base stat total with the exact same distribution, and both have only one possible ability[4][5].
| Stat | Silcoon | Cascoon |
|---|---|---|
| HP | 50 | 50 |
| Attack | 35 | 35 |
| Defense | 55 | 55 |
| Sp. Atk | 25 | 25 |
| Sp. Def | 25 | 25 |
| Speed | 15 | 15 |
| Ability | Shed Skin (only) | Shed Skin (only) |
| Total | 205 | 205 |
Neither cocoon can act in battle beyond Harden and a Shed-Skin status cure, and neither is worth catching for anything other than reaching level 10. If you’re just trying to fill a Pokédex entry or grind toward the final form, which cocoon you got is cosmetic — the real fork is what happens next.
Cascoon Evolves Into Dustox at Level 10
Once a Cascoon hits level 10, it evolves into Dustox automatically — no stone, no trade, no held item, just a level threshold[5]. The moment it evolves, it learns Gust, a Flying-type special move, worth noting because Dustox itself is pure Bug/Poison and never gains a Flying type of its own — the move is a legacy carryover shared with the Silcoon/Beautifly branch, not a hint about typing[6][8]. From there its level-up moveset continues with Confusion at 12, Poison Powder at 15, Moonlight at 17, and Venoshock at 20[6], giving it a status-and-recovery kit (Poison Powder plus Moonlight-fuelled stalling) rather than a hard-hitting one — a pattern that tracks with the stat spread below.
Beautifly vs. Dustox: How the Two Final Forms Actually Differ
By the time both lines reach their final stage, the identical-twin phase is over. Beautifly (Bug/Flying) and Dustox (Bug/Poison) diverge hard, and the gap is bigger than the 10-point base stat total difference suggests.
| Stat | Beautifly | Dustox |
|---|---|---|
| Type | Bug/Flying | Bug/Poison |
| HP | 60 | 60 |
| Attack | 70 | 50 |
| Defense | 50 | 70 |
| Sp. Atk | 100 | 50 |
| Sp. Def | 50 | 90 |
| Speed | 65 | 65 |
| Ability | Swarm / Rivalry (hidden) | Shield Dust / Compound Eyes (hidden) |
| Total | 395 | 385 |
| Best for | Special-attacking sweeps, low-tier speed-tie matchups | Special walling, status support, Poison-type utility |
| Avoid if | You need physical bulk — 50 Defense breaks against any physical attacker | You need raw damage — 50/50 offenses can’t threaten most Gen 3+ matchups |
Beautifly dumps almost everything into 100 Special Attack, the highest stat either line reaches, but its 50 Defense means it folds to physical pressure it can’t switch into safely. Dustox gives up 15 points of total stat and every point of offense to build a genuinely bulky special wall — 90 Special Defense is a 40-point gap over Beautifly’s 50, and paired with Shield Dust (which blocks secondary effects like burns and flinches) it’s a far more durable pick against special attackers than its lower base stat total implies. Neither outclasses the other; they’re built for opposite roles, and the stat total alone undersells how differently they play.
The movepools reinforce that split instead of blurring it. Beautifly’s line leans into direct pressure — its Bug/Flying typing and inflated Special Attack point toward a fast attacker role, even with a shallow movepool by modern standards. Dustox’s kit, by contrast, pairs Poison Powder (a status that cripples physical attackers over time) with Moonlight for sustained recovery, which is exactly the toolkit a 90 Special Defense stat is built to support: stall a hit, heal it off, repeat. If you’re deciding which one to actually train instead of just Dex-filling, ask whether your team already has a fast special attacker (favor Dustox for the role it’s missing) or a wall that can outlast Poison-type counters (favor Beautifly for the damage Dustox can’t provide).
Which Path Should You Actually Want? A Player-Type Breakdown
| Player type | Priority |
|---|---|
| New player | Don’t reset over this — either cocoon reaches a usable final form by level 10, and neither wastes meaningful playtime. |
| Casual player | Whichever you get, level it to 10 before deciding whether to keep it — the cocoon stage tells you nothing useful about the final form. |
| Hardcore / optimiser | If you specifically want Beautifly’s 100 Special Attack for a fast special sweeper, don’t trust a “day/night trick” in any game — catch multiple Wurmple and accept the roughly 50/50 split instead. |
| Completionist | You need both lines for a full Dex regardless of preference — catch at least two Wurmple per save file, since a 50/50 split means one Wurmple has roughly even odds of giving you a duplicate. |
For a sense of where this line sits on the power spectrum, it’s about as far as you can get from the Pokémon this site ranked among the game’s strongest three-stage lines — see our pseudo-legendary ranking for the other end of that scale. Wurmple’s line isn’t built to compete with them; it’s built to teach the personality-value mechanic to new players in the most low-stakes way the games have.
FAQ
Can shiny odds tell me which evolution I’ll get?
No — they’re derived from different parts of the same personality value, but shininess and the Silcoon/Cascoon split are independent calculations. A shiny Wurmple has the same 50/50-ish split as a normal one; one doesn’t predict the other.
If I already know a Wurmple’s nature, can I work out its evolution?
Not reliably. Nature and the evolution split both derive from the personality value, but through different bit ranges and different math — knowing one doesn’t let you reverse-engineer the other without tools most players don’t have access to mid-game. Treat them as separately random from a player’s perspective.
Does breeding two specific natures change what a bred Wurmple evolves into?
No. Breeding influences the offspring’s own personality value in ways that can bias nature (with an Everstone) or shininess (with Masuda Method / Shiny Charm stacking), but nothing in the breeding mechanic targets the Wurmple-specific evolution check — the offspring still gets its own fresh, unbiased personality value for that calculation.
Is Cascoon or Dustox ever worth using competitively?
Dustox has carved out a real niche as a cheap special wall in lower competitive tiers, largely off that 90 Special Defense and Shield Dust’s secondary-effect immunity — it’s not a top-tier pick, but it’s not a joke either. Cascoon itself never sees competitive use; it exists purely as a two-level bridge.
Why does Dustox learn a Flying-type move if it isn’t part Flying?
Because the Wurmple line’s level-up moveset was built once and shared across both branches rather than customized per final type. Gust made sense for Beautifly’s Bug/Flying kit, and rather than write a separate early move for Dustox, the games gave it the same one — it’s a quirk of shared movepool design, not a hint that Dustox has a secondary Flying typing anywhere in its Pokédex data[7].
Should I bother catching more than one Wurmple?
Yes, if you want both final forms on one save. Since the split sits close to 50/50 in every game, including Legends: Arceus, catching only one Wurmple gives you roughly even odds of getting the form you didn’t want. Two or three catches is usually enough to land both lines without relying on luck for a single specimen.
Version Verification
Mechanics and stats verified against Pokémon Database and Bulbapedia as of the current Scarlet/Violet and Legends: Arceus data. The personality-value split has been unchanged since Generation III, and no confirmed exception exists in any release, Legends: Arceus included — the day/night claim circulating for that game did not hold up under source-checking for this article. Revisit this if a future release documents a genuine, testable exception.
Sources
- Wurmple (Pokémon) — Bulbapedia
- Talk:Wurmple (Pokémon) — Bulbapedia
- Wurmple — Pokémon Database
- Silcoon — Pokémon Database
- Cascoon — Pokémon Database
- Dustox (Pokémon) — Bulbapedia
- Dustox Moves (Generation 6) — Pokémon Database
- Dustox — Pokémon Database
- Beautifly — Pokémon Database
- Pokémon Legends: Arceus — Wurmple Evolution Guide, ScreenRant
- Pokémon GO Wurmple Evolution Guide, Sportskeeda
- Wurmple Evolution, Pokémon Legends: Arceus — Gosunoob
I've been playing video games for over 20 years, spanning everything from early PC titles to modern open-world games. I started Switchblade Gaming to publish the kind of accurate, well-researched guides I always wanted to find — built on primary sources, tested in-game, and kept up to date after patches. I currently focus on Minecraft and Pokémon GO.