As mentioned in devlog #45 about Wisps, technologically and biologically influenced mutation and infection affect all arthropods–and some other creatures– differently. An order, family, genus, or species may branch off into several different new varieties. Titans are arthropods that, on the outside, resemble their original ancestors, except they are much bigger. Much, much bigger.
Of the titans left in the world, most bug-kin don't even know they're there. Titans hibernate for so long that their carapaces become one with the landscape. They rarely wake these days, although some beings and stimuli make it possible to rouse them. Witnessing hundreds of years of history, a titan can set the record straight on past local events or provide valuable insights, although they may just be cranky to be woken up.
While they look like massive versions of their ancient originators externally, they can have vast mutations internally. Many have developed bone structures in addition to their external carapaces and other advancements that have allowed them to move around their hulking frames or survive for hundreds of years. Some titan skeletons have been adopted as homes or ominous markers for travellers.
Adventurers, organizations, society, the weather– many things can affect how infection is spread or introduced. If that infection happens to be introduced to a hibernating titan, terrible consequences may ensue. They may wake, aggressive and confused, endangering locals, or their bodies simply succumb to the infection, feeding its progression.