It’s called a “sperm whale” because early whalers found a huge reservoir of milky-white, waxy oil in the whale’s massive head and thought it looked like sperm, so they named the substance “spermaceti” and started calling the animal the sperm whale.

Quick Scoop

The name’s odd origin

  • Inside a sperm whale’s giant square head is a huge organ filled with a white, waxy liquid now called spermaceti.
  • 18th–19th century whalers opened the head, saw this thick fluid, assumed it was semen, and nicknamed it “sperm oil” and “spermaceti,” which led to the common name “sperm whale.”

Why spermaceti mattered so much

  • Spermaceti was once extremely valuable; it was used for high‑quality candles, lamps, lubricants, soaps, and other products, so whalers specifically targeted these whales for that head oil.
  • Because the trade in spermaceti and sperm oil was so important, the nickname stuck and spread into science, popular culture, and classics like Moby-Dick , even after people realized the fluid was not actually reproductive.

A couple of extra naming facts

  • The species’ scientific name is Physeter macrocephalus , roughly “big‑headed blower,” referring to its enormous head and blowhole.
  • Sperm whales are also called cachalots , likely from old French words linked to their big teeth, pointing to their role as the largest toothed whales in the ocean.

TL;DR: Whalers found a big tank of white oil in the whale’s head, thought it looked like sperm, named it “spermaceti,” and the whale got stuck with the name “sperm whale.”

Information gathered from public forums or data available on the internet and portrayed here.