Tell your comforting tales of mad wizards if you like. Human perversity, after all, is small, but unnatural selection is the chain roaches' mother and perhaps yours too.
The small form is a blattid centipede of seven to twelve roaches, joined ass-to-mouth in descending order of size, moving and digesting as one. The chitin is as strong as human skin but give it four points of defense for small size and skittery inclinations, and it moves half as fast as you can trot. It does not have hit points, rather individual roaches, d6+6 of them. When you hit, one roach is squashed, plus one for every 4 damage you do, and roll d8-1 for how close to the head you hit, maximum = number of remaining roaches; all but that number of roaches scatter from the chain.
The main weapon of a small chain roach is disgust. On a successful hit ignoring armor it climbs on you. The next round and subsequent it has a 10% chance each of finding the mouth, nose, ear or nether orifices. Throwing off a roach chain requires a successful bare-hand hit, -2 if it is on your back parts. Invasion by roaches is completely attention-consuming and requires a saving throw to expel the roach chain. Each round you have a 5% chance of contracting disease from each roach chain on you and 15% from each roach chain in you.
On occasion multiple chain roaches will knit together to create a wide scarf roach of 5d6+6 individuals. Its statistics are similar, but more roaches. The front roaches will often acquire a couple of stabbing or slicing implements: broken knife blades, iron spikes, knitting needles, and soon. Thus, when crawling on you a scarf roach does not seek to invade, but instead stabs for d3 damage each time. The chance of infection per round is 10% if a scarf roach is just crawling on you and 20% if it has opened some wounds.
If ten or more roaches are scuttling around the area - either naturally or because some chain roaches have taken damage - any chain or scarf roach in the area will regenerate 1 roach per round from this pool.