[Spirochete]

These sloths may win in urban streets, but they will get their asses cut to ribbons in the countryside.

Which means they'll control urban "islands", since railroads, interstate highways, and pipelines all pass through the countryside. Inland urban areas under Sloth control would require a continual Berlin-style airlift.

[Gaffer]

They won’t work. They’ll try to roam. If you think ‘walking dead’ is SYFY, think again.