A few weeks ago, I got a call from my nearly 4 year old nephew during dinner. I could hear the excitement in his voice as he shouted into the phone about seeing worms in the water at the town dock. I asked him what color they were and he said they were all colors. This brought back a memory from my own childhood, a memory until this moment I wasn’t even sure was real. I remember seeing huge iridescent blue green worms swimming at the surface of the water, and then seeing them washed up dead on the beach the next day. I saw them that one time, and never again, causing me to think I had either imagined it or witnessed something very rare. Hearing my nephew’s excitement a couple fo things became clear, what I saw was indeed real, and that now my family has an official childhood rite of passage: witnessing the spawning swim of the sand worms.
As I said, these worms spend their lives in their burrows, only occasionally leaving to crawl along the bottom to find better digs, otherwise they are in the sediment. Things change however, when it is time to mate. The males undergo epitoky, their bodies change shape and structure in preparation for mating. They turn shimmery blue green and learn to swim, and around the new moon, they swim to the surface at high tide and release their sperm into the water column. That sperm makes its way down to the females who have remained in their burrows. They fertilize the eggs they have spent nearly a year developing in their bodies. Once the eggs are fertilized, the female excretes them on the surface of the sediment outside her burrow, where they develop, hatch and start a new generation of sand worms. After shedding sperm, the males die. After laying the eggs, the females die. Such is the life of a sand worm.
The moon is involved because the worms, both male and female are highly sensitive to photoperiod, and the development of the eggs begins a year before mating in response to changes in day length. Something about the combination of warming water in the spring, lengthening days, and darkness at night tells the males that the females are ready, but as far as I can tell, we can’t know for sure when the magic will happen. That is why it is such a good idea to be outside as much as you are able. You never know when you will stumble upon a certain flower blooming, a case of tiny spiders hatching, baby birds fledging, a lynx track in the snow, or hundreds of two foot long blue green worms swirling in the water doing their once in a life time dance.