Why Lightning Is So Much Deadlier for Animals Than It Is for Humans

Horses in a field with lightning in the background.
The electricity from a lightning strike travels from the ground and through a horse's entire body -- from back hoof to front hoof. hlopex/Shutterstock

You may have already seen the jarring video that's making the rounds on social media: A man walking his dogs near Houston, Texas, takes a direct hit from a bolt of lightning. He topples to the ground, unconscious. Fortunately, the man — Alex Coreas — survived his brush with a bolt out of the blue.

But in the video, you likely also noticed the dogs — those faithful friends who stand by us through thick and thin — head for the hills. And they don't look back.

Humans quickly come to the fallen man's aid. But the dogs? They want none of it.

The thing is, they had good reason to get out of Dodge. As dangerous as lightning is to humans, it packs an even deadlier wallop for animals.

Consider the case from earlier this year of a couple of giraffes at Lion Country Safari in Loxahatchee, Florida. They were struck and killed by lightning. There was shelter nearby, but they went and stuck their necks out in a storm. They both likely died from the same bolt.

How is that possible? According to CNN meteorologist Taylor Ward, the bolt probably hit the ground, and then rippled outward in a deadly shockwave — a far likelier scenario than each giraffe being struck by separate bolts of lightning.

Perhaps the most heartbreaking example of a single bolt's devastating impact on animals took place in Norway back in 2016. More than 300 reindeer were found dead on a mountain plateau. Again, just one bolt of lightning — and a powerful ground current that swept the whole herd in its shocking embrace.

How lightning strikes

"Lightning does not strike a point, it strikes an area," John Jensenius, a lightning safety specialist with the National Weather Service, tells The New York Times. "The physical flash you see strikes a point, but that lightning is radiating out as ground current and it's very deadly."

In the case of those unlucky reindeer, the bolt may have struck one or two of them directly. But it was the current on the ground that took down the herd.

It happens to humans, too. But, as in the case of Alex Coreas, they stand a better chance of surviving the shock. So why do animals get the worst of it?

It all comes down to grounding. Humans, being bipedal, have two points of contact with the Earth. That's a short, sharp circuit — electricity travels up one leg, jolts the heart, and then runs down the other leg.

Of course, in many cases, it's enough to kill a human. But the wider devastation among animals is likely due to how they're grounded: They have four points of contact. Reindeer hooves are also far apart. So, imagine a lightning bolt hitting the ground. Its energy looks for a path to travel. It finds a leg, travels up it, and then finds another leg. And another leg. And another leg.

Because animals have so many legs, and they're much farther apart, the charge intensifies. Electricity flows through them, and outward. In fact, Jensenius notes the reindeer only had to have their feet on the ground in a roughly 260-foot area to receive that fatal jolt.

What's more, when lightning strikes a human, there's a chance the charge goes up one leg and out the other, without necessarily frying any vital organs. When lightning crackles up an animal's front paw or hoof, it travels through its body, vitals and all, to reach the rear leg.

Here's how Volker Hinrichsen, a professor at Germany's Darmstadt University of Technology describes it to Deutsche Welle:

"Animals have wider steps, maybe 1.5 or two meters wide, so the step voltage is much higher. The current, if it flows through the front and back legs, will always flow through the animal's heart. So the risk of death is much higher for animals during such an event."

Saved, but not unscathed

You might wonder then how the bolt that struck Coreas left his dogs unscathed. As the Washington Post reports, that's likely because he absorbed the bolt directly. He may have been insulated by his raincoat. And if he was sweating or covered in any sort of moisture — including the rain itself — the charge could have traveled around his body rather than through it.

And while it was enough to do incredible damage to Coreas, the lightning bolt wasn't able to translate its energy into a ground current.

There's a good chance that by taking the one-in-a-billion direct hit from lightning — and by being soaked with rain — Coreas saved the lives of those dogs. Although, at a terrible cost.

According to a GoFundMe page set up by his family, Coreas still faces a long road to recovery.

He doesn't remember anything from the strike. But, as Coreas told ABC News, when he came to in a medical helicopter, his thoughts turned to his beloved dogs.

"The first thing that came into my mind — and I asked — was 'Where are my dogs at?'"

They're safe and sound. But perhaps just a little more reluctant to step outside in a storm.