you cant. you just have to avoid them. here's the deal , try to get to rat man but don't get in the flies way jump over them or when there above you going down run to rat man and they will leave you alone.
Once you enter the control room, climb past the rats at right to reach the final red control wheel. This will dump sludge on Ratman and the flies will attack you. Dodge them until you can jump to the large center pipe, and then to Ratman.
The rats and stinging flies are Ratman's loyal pets. When you try to catch him, you have to get past them. The way to do this is to reach the final red wheel in the sewer control room. Time your jumps to dodge the rats and find it at the upper right. When you turn the wheel, it dumps sludge on Ratman and scares off his flies. Unfortunately they will now attack you. Run and jump to avoid them, and use the large pipe at the center of the room to jump over to where Ratman is. Knock him down and cuff him.
When you face ratman and his rats and flies, climb to the red wheel at the upper right, which will dump sludge on Ratman. Jump quickly between the rats. Then avoid his flies to jump over to him and cuff him.
Ratman is hiding in the sewer under City Park, with his pet rats and stinging flies.
You have to get the flies away from Ratman to defeat him. Climb up past the three rats on the right side to reach the final red wheel. Click it to dump sludge on Ratman. Now the flies attack you, but you can dodge them long enough to jump to the large center pipe, and over to where Ratman is.
try running as fast as you can until you get to him
Once you climb past the rats and turn the upper red control wheel, the flies leave Ratman and attack you. You will have to elude them by rapidly running right, then left, to climb the large pipes at the center. From there you can leap left to where Ratman is, and handcuff him.
The flies stay around Ratman in the control room, and there is no way past them. However, you can get them to leave him: jump past the three rats at the upper right and turn the red control wheel. This dumps sludge on Ratman and chases the flies, but they attack you. Get away from them and jump to the large center pipe, from which you can jump over to Ratman and cuff him.
Once you have dumped sludge on Ratman, his rats run away. But the stinging flies will attack you. Avoid them long enough to jump to the large pipe at the center, then over to Ratman. Cuff him.
There is no such tool (it is a myth perpetuated by cheat sites). The way to capture Ratman is to reach the control wheel at the upper right. Once you are past the rats, turn the wheel to dump sludge on Ratman. Now the flies will leave him and attack you. Avoid them and jump over to cuff Ratman.
When you are trying to catch Ratman in the sewer under City Park, you can chase the flies from him by going right, climbing past the rats, and turning the red control wheel. This will dump some sludge on Ratman and the flies. However, they will now chase and sting you. You should run right to elude them, then quickly jump to the large pipe at the middle, from which you can reach Ratman and cuff him.
You have to make a series of three jumps between the rats to reach the red wheel at the upper right (to dump the sludge on Ratman). Then evade the flies and jump from the middle raised pipe over to cuff Ratman.