Halloween crabs signall the coming rainy season in Costa Rica.
Something skitters around my toes, a flash of black on the golden beach.
I jerk my foot back, then laugh at my reflex. It's only a crab, smaller than my fist. And though its colours are ghoulish – black carapace, orange legs, pallid purple claws and beady black eyes – I tell myself it's silly to be spooked by such a small creature.
I have no idea of the invasion to come.
Dusk falls. A crescent moon rises. Heat lightning flashes over the waters of Costa Rica's Gulf of Nicoya. I check the zipper on my tent, pitched in a narrow band of palm trees that separates the sand of Playa Quesera from the wooded hills of the Curu Wildlife Refuge. It is early April, the parched end of a long dry season. Every living thing is waiting for the rains, my kayaking guide, Bruce Smith, says as he chops chayote (a Mexican squash) for our small group's evening meal. The yellowed trees; the squat, black, inscrutable iguanas; the howler monkeys who wail from the high branches – they are all waiting for the first storm to break the dry spell.
And now the harbingers of rain are arriving. We can hear them stirring through the dry leaves on the forest floor. The Halloween crabs are coming.
We wake the next morning to find the beach transformed: The flat expanse of sand has erupted into hundreds of small hillocks. From the holes in the tops of these hillocks, Halloween crabs pop in and out, pushing out loads of sand in the crooks of their purple claws, and disappearing down the holes to fetch more.
For two days, the burrowing continues, as we speculate endlessly over morning camp-stove coffee and evening wine: What are they doing?
Our guide shares with us what he knows: The Halloween crabs live in the forest. Every year, around this time, they come down to the beach to lay their eggs. When the moon waxes full – exerting its most powerful gravitational force and pulling the tide to its highest point – the waves will wash the crab eggs into the ocean, where the larvae will hatch and begin the life cycle anew. Beyond that, Bruce knows one more fact: The arrival of the crabs always coincides with the onset of the rainy season.
Sure enough, that night a tropical thunderstorm splits the sky. Lightning strobes the silhouettes of the palm trees. Rain pours down on the thirsty jungle. And the crabs, as though summoned by the thunder, swarm from the forest onto the beach.
The next day, they are everywhere. No longer hundreds, but thousands – perhaps tens of thousands. The forest rustles with the sound of their spindly legs, crawling through the deadfall. They climb the tree trunks, cling to the bark, scale our tent poles, hide in our kayaks. They lurk in the corners of the wooden outhouse and beneath the rustic toilet seat, so that the men take to the bushes for all but the most dire emergencies, and women are left with the choice of braving hidden pincers in the lavatory, or crouching in the equally creepy underbrush.
By the time we return from paddling that afternoon, the crabs cover the beach like autumn leaves after a windstorm – so thick that in some places, we cannot see the sand. Some of them scuttle from burrow to burrow. Others continue their patient excavation work. Sometimes, one crab chases another out of its hole, brandishing purple pincers.
"Is anyone else feeling freaked out about sleeping here tonight?" I ask after chasing two crabs out of my tent. But Bruce pours the wine and some Costa Rican coffee liquor, and I am soothed into lying down to bed among my crustacean companions.
The next morning, as suddenly as they came, the Halloween crabs are gone. Only a few stragglers remain, clinging to tree trunks or standing guard at their burrows.
It is time for us to leave too. As we launch our kayaks into the Gulf of Nicoya, I feel lucky that my trip to Costa Rica turned out to be not just a vacation, but a chance to witness one of nature's miracles.
Special to The Globe and Mail
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