There are three insects in SLASH'EM, all represented by a, which possess the ability to multiply, without the aid of water or other external sources. These are the giant tick, the giant flea, and the giant louse. All only appear in the Lawful Quest, and none is particularly much of a threat, even in the large groups they can create.
The mechanics of their multiplication is similar to gremlins, in that each subsequent monster is created with half the hit points of the previous one. However, the maximum HP remain the same. None of these insects can use their multiplication attack when their HP is at 1, however, as they heal, they can start to multiply again. In this manner, they can slowly multiply indefinitely, after a quick initial burst of multiplication.
Since all the monsters created will have 1 HP for a while after the initial spasm of multiplication, it makes these insects almost a non-threat. None of them can deal any appreciable amount of damage, and one hit from anything will kill them. The biggest danger is that they might heal and start reproducing again; for this reason, it is worth destroying them as soon as you see them, simply to avoid having them fill up the level and impeding your movement.