Horseshoe crabs

Horseshoe crabs are a very ancient form of life. They have only one clotting factor in their blood, but it clots: so much for the 'irreducible complexity' of the clotting system.

Horseshoe crabs thrive in Delaware Bay on the east coast of the U.S. When they spawn, they lay tens of thousands of tiny eggs. Migrating birds feast on the eggs and regain their reserves for the rest of their journey. The crabs depend on spawning at the same time and laying more eggs than birds or fish can eat. That is, their strategy is one of overwhelming predators with plenty. Spawning cod and emerging cicadas use the same strategy. The cod lay more eggs into the water than the schools of hungry herring can eat. The cicadas provide more body than all the predators can eat. Thus some of each generation survives long enough to produce the next generation. The trouble is, it's a balance.

If 90 or 95 or 97% of all the eggs are eaten by predators, man comes along and says, "Look at all that going to waste! I'll just take 10% or 25% and nobody will miss it," The balance is now weighted on the side of population crash and perhaps extinction.

The cod stocks are not recovering from years of fishing: there are still more than enough hungry fish to eat practically all their spawn. The horseshoe crabs' eggs are taken by the ton for bait, for fertilizer, for pet food. They are even used to test drugs. The migrating birds still stop in their thousands to eat the eggs. How long will it be until their population crashes and the birds starve on their way north? Once again, people will be scratching their heads and saying, "But there seemed to be plenty! It can't be our fault."