From the Super Mario Wiki
Scutlets are tick-like creatures that appear as enemies in Mario & Luigi: Bowser's Inside Story. A large 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 boss. 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. If three or less Scutlets remain, then one Scutlet will slowly walk over to a brother. This can be countered by a hammer.
Names in Other Languages
||Composed by piojo (lice) and "-uela", a sufix that is used to mean "little" or "a bit".
||Pun on pegar (to stick) and cucaracha (cockroach)
||From the boss version's German name Betaling and the Italian diminutive suffix -lino