Islamic State militants have adopted a disturbing tactic in northern Iraq. The militants are packing hundreds of live scorpions into bombs and launching them into nearby towns.

Poisonous varieties of scorpions are packed into a 2-ft canister by the hundreds. The canister is then launched into populated areas, exploding on impact and scattering hundreds of the creatures among the panicking civilians.

“It’s madness. ISIS has improvised devices to launch them,” Hamish de Bretton-Gordon told The Mirror. Bretton-Gordon is the ex-head of chemical and biological weapons for the British Army and NATO. He has recently returned from Baghdad where he was advising security forces.

“Scorpions are robust – even if they are launched a couple of miles, when the canister breaks thousands are flung out and start crawling around,” he said. According to Bretton-Gordon, ISIS has taken credit for the attacks and promote the idea to spread fear around the country.

The bombs are not causing massive casualties. In fact, few are killed during these attacks. However, they are having a noticeable “psychological impact” on the populous.

“Some scorpions are very poisonous, but the main thing is creating fear,” said Bretton-Gordon.

Interestingly, this is not the first use of scorpions as weapons in Iraq. Thousands of years ago, the Iraqis used pots filled with scorpions as a major biological weapon against the invading Roman army.

In Greek Fire, Poison Arrows & Scorpion Bombs: Biological and Chemical Warfare in the Ancient World, author Adrienne Mayor describes this first recorded use of scorpions in the defense of the fortress city Hatra.

“It was the brute effectiveness of Hatra’s defensive biological and chemical weapons that overcame Roman morale, manpower and siege machines,” she writes.

The U.S. confirmed last week that it had launched 20 additional airstrikes against ISIS targets. The targets include raids near Sinjar, Qaim, Ramadi, Mosul and Samarra, as well as inside Kobane. Kobane has been under attack by ISIS since Mid-September when the group assaulted the city in an attempt to seize control, according to Dailymail UK. Kurdish YPG fighters along with American airstrikes have since pushed ISIS out of central Kobane.