Ivy is not a parasite it uses its 'suckers' like a drunk, for support only. As mentioned earlier it often grows on the walls of houses, there's not much succour in bricks and mortar. It also grows on dead trees. Popular belief is that the Ivy has killed the tree, this is not usually the case. As previously stated it is easier to remove whilst alive. When dead it just breaks when trying to pull it off, leaving lots of bits behind.
There's no such thing as a bad taste joke