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 is found inside Bowser's stomach 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. During the 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 however, 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. They are like the cockroach of the Mushroom Kingdom, seeing that they are found in Junker Cans.
Names in other languages