The Subst Worm is a crayfish-type Worm and an antagonist in episodes 39 and 40 of Kamen Rider Kabuto.
He was portrayed by Takako Igarashi and Norihito Ito.
Kamen Rider Kabuto
The Subst Worm originally served under the Uca Worm until the human identity she had copied resurfaced and overtook her original personality. After the Uca Worm reverted to "Rena Mamiya", Subst Worm attempted to eliminate her for "betraying the Worms". Eventually, he was destroyed by Hyper Kabuto with his Hyper Slash.
Kamen Rider G
One of the Shade operatives transformed into a Subst Worm alongside three other Shade agents who also assumed the forms of Worms to fight Kamen Rider G. All four of them were destroyed by G.
Kamen Rider Decade
World of Kabuto
The Subst Worm targeted Mayu, chasing her and Natsumi down until it is destroyed by a shockwave from Mayu's transformation into the Sisyra Worm.
Kamen Rider Decade: All Riders Vs. Dai-Shocker
The Subst Worm was among the monsters who were part of the Dai-Shocker army in the World of Decade. They fought against a gathering of 25 Kamen Riders who formed to oppose Dai-Shocker's invasion of the A.R. Worlds.
OOO, Den-O, All Riders: Let's Go Kamen Riders
In the alternate future where Shocker achieved their goal of world domination and defeated the Double Riders with their new kaijin Shocker Greeed, Subst Worm was one of the many monsters from future villain groups that were assimilated into Shocker's global regime.