999/1000 Chance of Failure
When the Decepticons created the Insecticons, the process they used to do so only had a 1/1000 chance of success. By the time Bombshell, Shrapnel, and Kickback were created, the Insecticon-creation failures had come to be around 3000 strong. These failures made up the Insecticon Swarm, mindless creatures that attack anything that isn't them. When the Decepticons left Cybertron, they released the Swarm as a way to clean Cybertron of any resistance that might remain.
Hunting the Autobots
When the Autobots were banished to Cybertron during the All Hail Megatron saga, the Insecticon swarm was their main problem. Knowing that they could not take them all on, the Autobots were forced to retreat whenever the Swarm came close to their base. After the Wreckers showed up, Hot Rod said that is was sheer luck that allowed them to avoid the Swarm. Shortly afterward, Preceptor and Drift killed two of them to demonstrate what they were capable of. Soon, the rest of the swarm attacked, and the Autobots had to blow up a bridge in order to buy some time in order to find a way back to Earth. Eventually, the Swarm caught up with them after crossing another bridge, and began to overwhelm the Autobots using their sheer numbers. Just before the Insecticon swarm consumed the Autobots, Omega Supreme arrived. With the giant guardian backing them up, the Autobots were able to counterattack. The Insecticon-failures that were not destroyed fled from Omega Supreme.
Two to three years later, Ironhide awoken sometime after he was killed on Earth. Two members of the Insecticon swarm ambushed him, but Ironhide killed him. Ironhide's next encounter with the Insecticon swarm was when he rescued Sunstreaker, who sacrificed himself in order to blow up the bridge from before. This time, Ironhide used defensive manuvers and simple drove away from them; occasionally slamming into walls in order to shake off any swarm member who managed to catch him. After delivering Sunstreaker to safety, Ironhide finally realized why he had been brought back to life: To purge Cybertron of the Insecticon swarm. Armed with this knowledge and some heavy weaponry, Ironhide set out to exterminate the Insecticon swarm. The battle that followed went like this:
1. Ironhide starts blasting away at the Swarm and then blowing up his battery pack once the Insecticon swarm started eating it.
2. Using the weapons in the Wrecker's ship to blast more of the swarm, followed by blowing it up when the buggers breached the walls.
3. Pulverizing the Insecticon swarm with his fists.
Once the swarm started to overwhelm Ironhide, he was forced to retreat, which prompted the Insecticon swarm to pursue him. Unfortunately, their efforts were rewarded in the form of Metroplex's hand crushing them. Unfortunately, this only meant that the main swarm was defeated, any pseudo-Insecticons that branched off from the main swarm were still roaming Cybertron. Ironhide and Sunstreaker were left on Cybertron to take care of the rest of the Insecticon Swarm.