CHATHAM, MASS. (WHDH) - A familiar sea creature that has helped save lives for decades may now need saving itself.  Early each summer, horseshoe crabs crawl up on Massachusetts beaches to mate.  “They are just lots of males here looking for some action,” one volunteer said.  This time of year gives volunteers a chance to count just how many crabs remain.  While horseshoe crabs outlived dinosaurs, their population along the East Coast drastically dipped in recent decades.  One reason for the statistics is they are caught for fishing bait, another main other reason…they are captured for their blood.  “You may not know it, but for the last 40 years we’ve been using purified horseshoe crab blood to ensure the safety of our medicine,” said Jay Bolden, senior director at Eli Lilly and Company. The crab’s unique blue blood reacts to dangerous bacteria.…