When Chelsea Wood was a child, she would often collect periwinkle snails on the shores of Long Island. “I used to pluck them off the rocks and put them in buckets and keep them as pets and then release them,” Wood said. “And I knew that species really well.” It wasn’t until years later that Wood learned that those snails were teeming with parasites. “In some populations, 100 percent of them are infected, and 50 percent of their biomass is parasite,” Wood said.
Jesse Nichols/Grist The parasites were a sign that the local shorebirds were doing great, Wood explained. As scientists have learned more about parasites, some have argued that many ecosystems might actually need them in order to thrive. “Parasites are a bellwether,” she said. “So if the parasites are there, you know that the rest of the hosts are there as well. And in that way they signal about the health of the ecosystem.
Jesse Nichols/Grist Wood and her team spent over two years opening up jars and surgically dissecting the parasites from within. Under microscopes, they identified and counted the parasites before returning everything for future study. In the end, they found more than 17,000 parasites.