Why Was Purple the Color of Royalty? And More Questions From Our Readers

Q: I’ve heard that purple was called the royal color because purple dye used to be scarce. Why didn’t people just combine blue and red? Dan Warnock | Baker City, Oregon

Many purples in historic fabrics are, in fact, the result of coloring a fabric with a blue dye, like indigo or woad, and a red dye, like madder. But the “Tyrian purple” associated with royalty—believed to have originated in Phoenicia (modern Lebanon) as early as 1200 B.C.—was made by extracting mucus from snails found along the Mediterranean Sea through an expensive, labor-intensive process. Ancient writings suggest this dye was desirable not only for its brilliant hue, but also for its ability to stay colorfast over time. Similar sea snails are found across the world, and some cultures, like the Mixtec weavers in Oaxaca, Mexico, still use them for dyes today. —Jennifer Cohlman Bracchi, head librarian, Cooper Hewitt, Smithsonian Design Museum

Q: Are there any invasive species that have actually improved U.S. ecosystems? Frank Gregorio | Manassas, Virginia

The short answer is no, since invasive species are, by definition, species that threaten the native ecosystem. Many arrive accidentally, stowing away in containers or escaping gardens. Sometimes non-native species are introduced with good intentions—for instance, to help prevent soil erosion or to keep other non-native species under control. But anytime a non-native species is introduced to an ecosystem, there’s a risk that the newcomer will replace local species by attacking or outcompeting them. The best approach is to avoid introducing them altogether. —Gary Krupnick, head of the Plant Conservation Unit, National Museum of Natural History

Q: How did the body of a violin get its shape? Edwin Anderson | Glendora, California

Bowed instruments have existed for more than a thousand years, but early examples, like those found in Arab lands, had only a few strings and lacked a narrow “waist.” By the 1400s, instrument makers in Spain were building viola da gambas with as many as seven strings. These instruments were built with narrow waists so musicians could bow the top and bottom strings without hitting the sides. It’s generally accepted that Andrea Amati in Cremona, Italy, built the first four-string violin in the 16th century, following the general shape of the viola da gamba. The violin family (including violin, viola and cello) was refined by his grandson, Nicolo Amati, and Nicolo’s followers, including Antonio Stradivari. —Gary Sturm, curator emeritus, National Museum of American History

Q: Does the brain of a butterfly or moth retain memories from when it was a caterpillar? Philip G. Grant | Pasadena, California

We once believed metamorphosis completely dissolved the caterpillar and rearranged its components. But in a study published in 2008, caterpillars were trained to associate the smell of ethyl acetate with a mild electrical shock. Emerging adults showed a similar aversion to the smell of ethyl acetate without a shock as they did as larvae when paired with the shock, suggesting that some synaptic pathways had been retained. So, while adult moths and butterflies probably don’t remember the details of what it was like to be a caterpillar, certain associative memories can persist into adulthood. —Floyd Shockley, entomology collections manager, National Museum of Natural History