They would pack clay pots full of scorpions and hurl them at Roman armies

in the desert city of Hatra in 198-199AD

The tactic was first used by

They do not cause mass

packed with the creatures are being blasted into Iraqi towns

Canisters packed with poisonous varieties of scorpion are being blasted into towns and villages - scattering the creatures and inciting panic

Militants fighting for the Islamic State in Iraq have unveiled their latest terror tactic - bombs containing hundreds of live scorpions designed to spread fear among their enemies.

Canisters packed with poisonous varieties of scorpion are being blasted into towns and villages, which explode on impact - scattering the scorpions and causing panic among the innocent local population.

Although scorpion bombs sound like something out of a modern horror movie, the tactic is actually thousands of years old and was first used by Iraqis fighting against the Roman Empire.

Hamish de Bretton-Gordon, ex-head of chemical and biological weapons for the Army and Nato, told The Mirror that ISIS had improvised devices to launch the poisonous creatures in 2ft bombs.

He said: 'Scorpions are robust – even if they are launched a couple of miles, when the canister breaks thousands are flung out and start crawling all around.

'Some scorpions are very poisonous but the main thing is creating fear.'

Mr de Bretton-Gordon, who returned from Baghdad last week where he was advising security forces, said that the bombs are not causing casualties but had a profound 'psychological impact'.

The bizarre biological weapon was used as far back as 198 AD, when Iraqis stuffed live scorpions into ceramic pots and hurled them at Roman armies marching on the fortress city of Hatra.

The Parthian city was held under siege for 20 days by Emperor Septimius Severus before the Roman military were driven out by the 'live grenades'.

Militants fighting for the Islamic State in Iraq have unveiled their latest terror tactic - bombs containing hundreds of live scorpions designed to spread fear among their enemies

Adrienne Mayor, a historian of ancient science and classical folklorist, researched the weapon in detail for her 2004 book Greek Fire, Poison Arrows & Scorpion Bombs: Biological and Chemical Warfare in the Ancient World.

SCORPION BOMBS - 'THE WORLD'S OLDEST BIOLOGICAL WEAPON' The live grenades were first used by Iraqis in the besieged city of Hatra in 198-199AD. Soldiers would pack ceramic pots full of live scorpions which they would then hurl at the Romans led by Emperor Septimius Severus. It is thought that they would first spit on the scorpions to slow them down so they could be handled - although it was still an incredibly risking tactic. The biological weapon has been credited with ending the 20 day siege on the desert city. Advertisement

She describes how soldiers would spit on the end of the scorpion to calm the creatures before they were packed into pots, which were flung at the besieging Romans.

'It was the brute effectiveness of Hatra's defensive biological and chemical weapons that overcame Roman morale, manpower and siege machines,' she writes. 'The terror effect would be quite impressive.'

Last week, the U.S. confirmed it had launched a further 20 airstrikes against ISIS targets, including raids near Sinjar, Qaim, Ramadi, Mosul and Samarra, as well as inside Kobane.

ISIS militants have been attacking the Iraqi town of Kobane since mid-September, when the terror group assaulted its southern suburbs in an attempt to seize control of the strategic border city.

The terror group quickly encircled the city, raping and murdering its inhabitants, but Kurdish YPG fighters supported by U.S. airstrikes have since pushed ISIS back out of central Kobane.