The color purple, and the feeding ecology of a snail

by Christopher Oxley

Tyrian purple is a dye known by many names: shellfish purple, purple of the ancients, royal purple and 6,6’-Dibromoindigo. It is a beautiful, extremely lightfast reddish-purple pigment, which becomes darker and more saturated rather than fading over time. The rich color and these unique traits made Tyrian purple and the snail it comes from highly coveted. The remnants of a thousand year old purple dye economy can be used along with modern studies to reveal the feeding ecology of this snail (Cooksey 2001).

Tyrian purple mostly came from the murex snail, Hexaplex trunculus, commonly known as the Banded dye-Murex. The harvesting of H. trunculus for its dye may have originated in Crete, but the industry grew during the Phoenician trading empire and reached its apex during the Roman and Byzantine empires. Each snail only produced a very small amount of dye, so to meet demands, the Banded dye-murex snails were collected en masse. Pliny the Elder wrote in the collection of works known as Natural History that small amounts of these snails could be harvested by hand from rocky coastlines or by diving; however, larger quantities were collected using a nassae, a type of baited trap. This resulted in large, relatively well-preserved middens. Today they help to reveal more about ancient harvesting practices and show how knowledge of the ecology of H. trunculus was exploited (Oliver 2015).


Shell of Hexaplex trunculus from Wikimedia commons.  

An analysis of a midden in Motya, Sicily suggests that sperm whale vertebrae may have been used as a platform to crush snail shells so that the dye within could be retrieved (Reese 2005). The abundance of shells from small juvenile snails in the top layers of a midden in Lycia, Turkey reflect the classic signs of a population that has been steadily overexploited, possibly resulting in the eventual extinguishment of the purple dye economy in the region (Forstenpointner et al. 2007).

Analyses of other animal remains within these middens can also help to reveal what bait was used to trap the Purple dye Murex and reflects its feeding strategies. A midden found on the island of Palma has a relatively high concentration of the snail Cerithium vulgatum found in combination with the remains of H. trunculus. Banded dye-murex snails are predators of other mollusks. They commonly attack their prey by drilling holes in the prey item’s shell and inserting their proboscis to feed. Multiple drilling attempts are present on the C. vulgatum shells suggesting that they lived in an environment with numerous predators, meaning they were likely used as bait in a nassae. The borehole attempts also suggest that the Banded dye-murex prefers to drill into the first few whorls of its prey just after the apex of the shell (Oliver 2015). Thus, the prey species found in ancient middens may be a significant starting point to understanding the feeding ecology of H. trunculus.

H. trunculus has become the focus of many modern ecologists due to its abundance across the Mediterannean and importance as a benthic predator. Research by Peharda & Morton revealed that the Banded dye-murex avoids bivalves with a dense periostracum, the living, outer layer of the shell. As the Banded dye-murex matures, it even uses various feeding methods (Peharda & Morton 2006). Like other murexes, it relies on its radula to rasp through the shell of its prey with the aid of acidic secretions, but larger Banded dye-murexes can also use a method of marginal chipping. H. trunculus was observed to position the lip of its shell against the outer edge of a bivalve to break pieces off and allow insertion of its proboscis (Morton & Peharda 2007).


Shell of Cerithium vulgatum from Wikimedia commons.

By understanding the history behind the Banded-dye murex, its feeding ecology can be revealed, and by understanding its feeding methods, the archaeological remains of H. trunculus can be better interpreted. Exploring all the aspects of an organism, even its historical presence, or cultural impact can provide perspective and benefit ecological research.


Cooksey, C. (2001). Tyrian purple: 6, 6’-dibromoindigo and related compounds. Molecules6(9), 736-769.

Forstenpointner, G., Quatember, U., Galik, A., Weissengruber, G., & Konecny, A. (2007).

Purple‐dye production in Lycia–results of an archaeozoological field survey in Andriake (south‐west Turkey). Oxford journal of archaeology26(2), 201-214.

Morton, B., Peharda, M., & Harper, E. M. (2007). Drilling and chipping patterns of bivalve prey predation by Hexaplex trunculus (Mollusca: Gastropoda: Muricidae). Journal of the Marine Biological Association of the United Kingdom, 87(4), 933-940

Oliver, A. V. (2015). An ancient fishery of Banded dye-murex (Hexaplex trunculus): zooarchaeological evidence from the Roman city of Pollentia (Mallorca, Western Mediterranean). Journal of Archaeological Science54, 1-7.

Peharda, M., & Morton, B. (2006). Experimental prey species preferences of Hexaplex trunculus

(Gastropoda: Muricidae) and predator–prey interactions with the Black mussel Mytilus galloprovincialis (Bivalvia: Mytilidae). Marine Biology148(5), 1011-1019.

Reese, D. S. (2005). Whale bones and shell purple‐dye at Motya (western Sicily, Italy). Oxford  Journal of Archaeology24(2), 107-114.

Author Biography: Christopher Oxley is an undergraduate student studying marine biology at Texas A&M at Galveston.

Categories: Science

Tagged as: , , , ,