measuringworm

[mezh-er-ing-wurm] /ˈmɛʒ ər ɪŋˌwɜrm/
noun
1.
the larva of any geometrid moth, which progresses by bringing the rear end of the body forward and then advancing the front end.
Also, measuring worm.
Also called inchworm, looper, spanworm.
Origin
1835-45, Americanism; measuring + worm