Caterpillar and Looper

Caterpillar noun - A large tracked vehicle that is propelled by two endless metal belts; frequently used for moving earth in construction and farm work.

Looper and caterpillar are semantically related. In some cases you can replace term "Looper" with "Caterpillar", this nouns are similar.

Looper noun - Small hairless caterpillar having legs on only its front and rear segments; mostly larvae of moths of the family Geometridae.

Caterpillar and looper are semantically related. You can use "Caterpillar" instead a noun "Looper".