A wild boar runs through the grounds of a Kyoto University dormitory in the western Japan city of Kyoto on June 13, 2017. The 1-meter boar was caught about an hour later. (Kyodo) ==Kyodo (Photo by Kyodo News via Getty Images)

Rapidly shrinking towns and cities across Japan are experiencing a population explosion. Not an explosion of humans, though. An explosion in wild boar numbers.

Across the country, wild boars are moving in as Japan’s rapidly aging population either moves out or dies out. The boars come for the untended rice paddies and stay for the abandoned shelters.

“Thirty years ago, crows were the biggest problem around here,” said Hideo Numata, a farmer in Hiraizumi, human population 7,803, precise boar population unknown.

“But now we have these animals and not enough people to scare them away,” he said, sitting in a hut with a wood stove and two farmer friends. At 67, Numata is a relative youngster around here. His friends, Etsuro Sugawa and Shoichi Chiba, are 69 and 70 respectively. One of their farmer neighbors is 83.

Southern parts of Japan have had a wild boar problem for some years. The papers are full of reports of boars in train stations and parking garages, around school dormitories and even in the sea, swimming out to islands.

Just this month, a 70-something woman was attacked on Shikoku Island by a 176-pound boar when she opened her front door. A boar charged into a shopping mall on the island last October, biting five employees and rampaging through the aisles before being captured.

In Kyoto, at least 10 wild boars were spotted in urban areas last year. Two charged into a high school in December, causing panic and the students to be evacuated.

But the animals are now wreaking havoc in northern areas long considered too cold and snowy for them.

Here in Iwate Prefecture, only two wild boars were caught in 2011, when local authorities started keeping statistics. In the last fiscal year, that number had skyrocketed to 94.

The influx is the result of two factors, experts say: declining human populations and climate change.

Japan’s regions are struggling to deal with dwindling numbers of residents, the result of a super-aging society — 40 percent of the population will be older than 65 by 2050 — and a national trend toward moving to the big cities in the south.

Farmers are dying and there is no one to take over their land. Take Sugawa and Chiba: They both have sons but they’re salarymen in the city with no interest in a hard life tending fields and fending off animals heavier than themselves.

This northern region has been hit particularly hard by depopulation. People were forced out when the gigantic 2011 earthquake caused a triple meltdown at the Fukushima nuclear plant, and after the resulting tsunami wiped out coastal towns.

Much of the area remains inhospitable for humans, but perfect for boars.

“Because of depopulation, there are more and more abandoned fields and rice paddies. They’re perfect places for wild boars to hide and feed,” said Koichi Kaji, professor of wildlife management at Tokyo University of Agriculture and Technology.

With reports of boars rampaging through the ghost towns around the Fukushima plant, some people worry if the animals are becoming radioactive.

In addition to depopulation, another factor for the boar explosion: The winters are also getting markedly warmer. “We used to have much more snow than this,” Numata said, looking out as snowflakes fell gently on the fields.

The boars arrived like a plague here in 2015. “We heard rumors a few years ago that the wild boars were closing in on this area. And it wasn’t long before we started seeing them,” Sugawa said.

The boars are most evident by the damage they cause. Farmers wake up to find their carefully tended rice paddies have been trampled or their wheat and potatoes eaten.

In Hiraizumi, inland from the coast where the massive tsunami came ashore in 2011, the cost of the damage caused by wild boars rose sixfold between 2015 and 2016. Last month, farmers in nearby Shizukuishi caught a male that weighed a giant 280 pounds. 

The boars have even been spotted as far north as Aomori, at the snowy northern tip of Japan’s main island, Honshu.

Local authorities have been offering subsidies to help farmers put up electric fences and keep the boars out of their fields, although this is a challenge given that there are so few able-bodied people to do the work.

The authorities have also been encouraging locals to get the necessary permits needed to trap and kill the animals. The town council even offers shuttle buses so they can take the required tests for permits in the prefectural capital.

This is where Japan’s aging population and its love of paperwork collide. 

To cull the wild boars, farmers need to obtain not just a gun license — an exhaustive process that involves medical certificates and gun storage inspections by the local police — but also a special license to lay traps. This involves intensive study for a written test — the local university offers classes for the farmers — as well as a practical exam for using different kinds of traps. 

Only then can the farmers capture the boars and shoot the animals they catch. 

Hiraizumi has about 10 people with the right paperwork to take on the boars and they catch only one or two boars a month, and only between November and March. (To cull them during the other months, they need yet another permit.)

“The lack of manpower here is a real problem,” said Rise Suzuki, the Hiraizumi town official in charge of the anti-boar campaign. “We need farmers to protect their own land and to take action against the boars, but it’s difficult for them because most of them are old.”

If it’s difficult to capture the existing animals, it’s even more difficult to stop them from breeding.

The wild boars have a huge reproductive advantage over the human population.

The average Japanese woman gives birth to 1.44 babies in her lifetime but the average wild boar has 4.5 babies a year. And those piglets reach breeding age in only two years, so the problem is only going to get worse. 

In Hiraizumi, officials and farmers alike are now gearing up for the spring, when piglets will be born and the mothers will be hungry.

“Local residents need to step up and do their bit to protect their fields and keep the boars from coming here,” said Chiba. But for now, the farmers are realistic about the challenges they face. As Sugawa put it: “Our rural areas are in decline.”

Yuki Oda contributed to this report.