For decades, biodiversity has been known to peak near the equator. But a new study reveals a striking exception: certain trematode parasites are more common in cooler, temperate waters. By tracking infections across snails, crabs and fish, researchers found that host movement, local conditions and temperature shape where parasites thrive. In warmer regions, infections are more lethal; in cooler waters, hosts survive longer, allowing parasites to persist – offering new insight into how ecosystems function and how disease may shift with climate change.