"We were hopelessly overrun as more of the amalgamate came in, as we killed one 2 more would take its place."
Amalgamate hosts are a sub sect of the infection forms, easily identified by the smaller parasites that grow from their backs. They usually have a much longer head than usual, the back of it usually resembling the form of the parasites, more often than not however the majority of it may be under some sort of plating or protection. Indeed the majority of hosts are created when an individual is assimilated by a parasite, otherwise hosts are rarely seen. It seems that the amalgamate requires a specific sort of individual or a mind to be able to create this variant of itself, as a singular assimilated mind wouldn't be able to control anything more than itself from the get go. It is unclear what causes an individual to be compatible of becoming a host however. If an individual isn't compatible to becoming a host the amalgamate tends to follow their common logic of assimilating the infected individuals biomass to a brood or turning them into a more common infection form.
The main function of this form of amalgamate is to carry smaller amalgamate forms to various places away from the broods. The smaller the amalgamate forms go, the less distance they can travel from the broods before exhausting their energy completely. Re-energizing these smaller forms alone away from a brood would also be rather inefficient and time consuming due to their lack of area capable of absorbing sunlight, heat and other forms of energy. The hosts however are able to carry these smaller forms much farther, allowing them to cause distress and disturbance in areas where they wouldn't be expected. The hosts are capable of also regrowing more smaller amalgamate forms, granted that they have the biomass for it. This alone makes hosts a priority target if seen, as they can produce smaller amalgamate without the assistance of a brood. The hosts however tend to avoid direct confrontation, even if their brood is discovered, instead relying on the parasites to do their bidding, perhaps to seek out and create more hosts.