Very little is known about the biology of Titanus giganteus, though it probably has a very similar life cycle to other members of the subfamily, including the Tanner Beetle Prionus coriarius, a small relative that is widespread (though rare) in southern Britain.
Most prioninae feed as larvae in buried decaying wood, probably for several years, with adults emerging for a brief annual flight period during which they reproduce and die.
The adults of most species in this group are thought not to eat. Dr Michael Balke brought back a live male Titanus from French Guiana, which lived for a few weeks and is now in the Natural History Museum collection - this is approximately the adult life expectancy for many large beetles. During this time it was rather active, and could be induced to fly if the temperature was high enough. But it could not be persuaded to eat - it was offered fruit and tissue soaked in sugar solution, and was occasionally seen to mouth these substances, though not to actively feed.
It is not uncommon for adult insects to survive entirely on resources stored during the larval stage, and some, for example many silk moths, completely lack a mouth and intestine.
Adult males have an impressive threat display when disturbed:
If carelessly handled, they can scratch the fingers with their defensive spines. Like the British stag beetle, it is best to avoid putting fingers directly into the jaws of a large living specimen! However, all of this behaviour is entirely defensive and the beetle will try to escape before resorting to this threat display.
It is not known what the natural predators of Titanus giganteus are, but these may include: