Giant hornets are stirring up trouble in China.

Health officials are reporting a number of hornet attacks that have killed at least 18 people in central China, the Associated Press reports. More than 100 in the city of Angkang in Shaanxi province have been stung by swarms of the flying insects and treated at Ankang City Central Hospital.

The South China Morning Post reports that there have been 28 deaths in the province.

“Patients with more than 10 hornet stings should seek medical attention. Those with more than 30 stings need immediate emergency treatment,” a director of Ankang Disease Control Centre told the local news outlet, Chinese Business.

The attacks, which have increased within the past three months, have also taken place in the cities of Hanzhong and Shangluo. Victims have been chased for hundreds of yards by the flying insects and been stung as many as 200 times, according to local reports.

While hornet attacks in the region aren’t unusual. According to Ankang police, 36 people died in the city and 715 were injured by the creatures between 2002 and 2005. This year has been particularly severe, possibly due to rising temperatures that allows the hornets to breed for longer periods of time.

In the latest wave of attacks, a 55-year-old woman said she spent a month in the hospital recovering from more than 200 stings. A man in her village died from kidney failure after the hornets chased him for more than 200 yards, the South China Morning News reports.

In Ankang, the fire department has destroyed 300 hornet nests. In other areas, local officials have warned residents to be “to be very vigilant while in the woods” and have offered to pay for medical treatment if they get stung.

Hornets, a type of wasp native to tropical Asia, don’t attack unless their nests are poisoned or destroyed. But their stings can have a deadly effect on humans, in some cases causing dangerous allergic reactions, according to National Geographic.

In China, the Asian giant hornet or Vespa mandarinia – the largest species of hornet in the world – may be the culprit of the attacks. The thumb-sized insects known for their fearless and aggressive behavior, have incredibly painful stings. "[The sting] was like a hot nail through my leg," Masato Ono, an entomologist at Tamagawa University, near Tokyo, said.  

Ankang experienced a wave of wasp attacks in 2005. At the time, officials said deforestation was the cause behind the attacks that killed 10 and injured more than 40 people. "Many trees where the wasps used to nest were cut for farming development a decade ago, now the insects have to live in trees near the villages," Lian Huisheng, a local township official, told China Daily.