From the Super Mario Wiki
Scutlets are cockroach-like creatures that appear as enemies in Mario & Luigi: Bowser's Inside Story. A larger member of the species that is also named Scutlet in English, Latin Spanish, French and Italian is found inside Bowser's Flame Pipe as a boss Mario and Luigi have to face.
More Scutlets appear outside of Bowser's body in Dimble Wood, which are much smaller than the one found in Bowser's body. For Bowser, they can be defeated in one hit for extra coins in the overworld, meaning they are exclusive for the Mario Bros. to battle normally. In battle, they appear in high numbers, and will attack by running at the Bros., showing which one they're going to attack beforehand. The attack is countered by jumping. Failing may give the Mario Bros. the Trip status effect. If three or less Scutlets remain, then one Scutlet will slowly walk over to a brother. This can be countered by a hammer. When Luigi is inside the giant Sockop, he must defeat four Scutlets.
Fittingly, Scutlets can be found in Junker Cans, as shown during the fight against Junker. In the Junker X battle, the Scutlets that come out of the Junker Can Xs are brown instead of the regular black.
Scutlets return in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, where they additionally are found as enemies in the Bowser Jr.'s Journey mode.
Profiles and statistics
Mario & Luigi: Bowser's Inside Story / Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
Names in other languages