BRUNSWICK — A spring full moon is always amazing to see, as it rises late in the evening just as the sun sets, bringing a feeling that summer is arriving. It also brings high tides. And, it brings horseshoe crabs. They are truly some of the strangest creatures out there.

The Atlantic Horseshoe Crab (Limulus polyphemus) has been around for about 450 million years. They are part of the Xiphosura class, one of the oldest groups of marine arthropods that is thought to have evolved in the shallow seas of the Paleozoic Era.

Over those many millions of years, however, horseshoe crabs have hardly changed. Perhaps it is because they are so well designed for survival. Their oversized carapace protects them as they cruise around the bottom like army tanks. Their copper-laden blue blood has amazing antibiotic properties and is used in medical testing to detect bacteria. And their tails have night vision — more than 1,000 light receptors let them “see” at night.

Oh, and they can also live out of water for four days.

Every fifth-grader from Brunswick’s Harriet Beecher Stowe Elementary School had the chance to see these creatures up close last week thanks to a field trip organized by the fifth-grade science team. Over the course of two days, buses arrived at Thomas Point Beach filled with students donning shorts and water shoes, ready to wade out and watch the cruisers.

Grouped into teams and armed with clipboards, the students cycled through stations where they learned about beach ecology, completed a seaside scavenger hunt, waded with the crabs, and took a break to play whiffle ball. Parent volunteers helped out at each of the stations, corralling the excited students and helping them to ask questions about what they were learning.

Some of the students had a chance to learn about horseshoe crabs ahead of time with their science teacher, Maria Palopoli, the originator of this field trip. She is not a marine biologist, but is instead a bug enthusiast. She runs an often sold-out bug camp over the summer where students learn to identify and mount insects to create their own bug collection.

I had a chance to see her collection last summer and it was amazing – everything from giant shiny beetles to tiny, delicate dragonflies. The connection to horseshoe crabs is that they are arthropods (invertebrate animals with a hard exoskeleton) as are insects.

You may have heard people call lobsters “bugs” and this is for the same reason. But, horseshoe crabs are chelicerates, not crustaceans (like lobsters), because of their chelicerae, a pair of small appendages used to put food into their mouths. In spiders, these often have venom!

When we first arrived at the beach, we immediately saw dozens of horseshoe crabs all cruising around in the shallow water. The reason for this has to do with that spring full moon. Every year in May and June, once the waters begin to warm a bit, horseshoe crabs come into shallow, warm waters to mate. They wait for the full moon when the tides are lowest and they can lay their eggs on the shore.

The crabs mate in a strange way that is amusing to see — the male latches on to the female and can stay attached for weeks. In fact, sometimes multiple males will latch on to one female, just waiting for the moment that she crawls up to the sand and lays her eggs.

The males have well-developed hooks on their first pair of legs perfectly designed to latch on to the female. These male “boxing gloves” are one simple way to tell the genders apart — females have a much thinner set of pincers.

The female waits for low tide and crawls up onto the sand. Then, she digs a depression in the sand and lays her eggs, at which point the lucky male who’s still around fertilizes them. Those that don’t get eaten first by shorebirds will hatch in a couple of weeks.

When high tide comes again, the baby horseshoe crabs will be swept out into the water.

For these fifth graders, this is a remarkable experience. Not only are they seeing something rare and prehistoric, but they are getting out to the coast that is so close to home. For some of them, this might be their first time. That is more amazing to me than the horseshoe crabs themselves.

Now students will return to their classroom to follow up on what they have learned, inspired by a special place and occurrence in their own town. If you want to experience this too, make plans for the June full moon and seek out a shallow intertidal area with sandy or soft sediment shoreline.