CSI: Crayfish Scene Investigation

The Case of the Wandering Crayfish…by Lesley McLaren

Like many investigations, this one began by accident.

June 1st, on a walk through the vineyards and orchards between Palau del Vidre and Laroque des Albères, I was about to cut a corner and cross a ditch between two vineyards.

A woodchat shrike often hunts there, and normally I would have been scanning the area for birds. But the grass was long after weeks of rain, the day was already hot, and I found myself watching the ground instead.

A sensible precaution, I thought. Perfect snake weather.

It turned out I was looking for the wrong suspect.

 I kept my dog behind me. A wise move, as it turned out, because a few metres ahead something small and dark was approaching us along the track.

Not slithering.

Walking.

What on earth was it?

Surely it couldn’t be…

A lobster?

Had the sun got to me?

No. It was a crayfish, about the size of my hand.

I stopped. It stopped. When I bent for a closer look, it tucked its tail beneath its body and reared up, claws raised in a posture that said quite clearly: “Come any closer and you’ll regret it.”

What was a crayfish doing here, hundreds of metres from the nearest pond?

Had a heron dropped it? If so, it seemed remarkably uninjured. Had it walked all this way? If it had, where was it going? And why?

The mystery deepened a few days later when my dog discovered the empty shell of a crayfish near the same track. Ants had probably finished off what remained. I felt a twinge of guilt. Should I have helped the first one? Had it become tangled in the vegetation and baked in the sun? Or fallen victim to another dog?

Then, days later, my dog found another crayfish—this time dead—in a grassy verge even farther from the pond.

One crayfish might be a curiosity.

Two looked like a pattern.

It was time to investigate.

The culprit turned out to be the Red Swamp Crayfish, or Écrevisse de Louisiane—an invasive species originally from the southeastern United States and Mexico. Introduced to Europe to compensate for declining native crayfish populations, they escaped from farms, were released from aquaria, and spread with help from unwitting accomplices such as herons.

Further digging revealed an important clue: these crayfish are accomplished travellers. During the breeding season, males embark on remarkable overland journeys. One recorded individual covered 17 kilometres in just four days.

Aha.

Perhaps the crayfish I’d encountered wasn’t lost at all. Perhaps he knew exactly where he was going.

Still, I’d never seen crayfish wandering through the vineyards before. The exceptionally wet weather seemed suspicious. So after yet another night of rain, I decided to see whether more evidence would emerge.

It did.

Driving along the lane between Laroque and Sorède, I spotted another crayfish crossing the road.

When I stopped, it stopped.

When I approached, it adopted the same martial-arts stance as its predecessor, brandishing claws with unmistakable intent.

This presented a problem.

By now I knew these crayfish can have a significant impact on local ecosystems. They reproduce rapidly, prey on a wide range of native species, spread crayfish plague, and undermine riverbanks with their burrowing.

Yet I couldn’t bring myself to run it over.

Unfortunately, I’d forgotten my Kevlar gloves again.

What followed was less wildlife management and more slapstick comedy. Attempts to pick it up by the tail were met with alarming flexibility and determined counter-attacks. Eventually, armed only with a mobile phone and questionable judgement, I managed to flick, scoop and nudge the furious crustacean off the tarmac and into the grass.

The crayfish survived.

My dignity barely did.

Case closed? Not entirely.

The evidence suggests that these wandering crayfish are now a familiar part of the local landscape, especially after wet weather. Whether marching in search of mates or new territory, they’re conducting their own quiet invasion beneath our noses.

So if you venture into the vineyards after rain, don’t be surprised if you find yourself face-to-face with a pugnacious crustacean from Louisiana.

Just remember one thing.

Bring the Kevlar gloves.