Five spikes are the secondary ingredient to extreme ranging potions. They can also be used to make headless arrows, though this is inadvisable due to their high cost.
Grenwall hunting has the potential to be profitable, making up to 161,000,000 coins from 77-99 Hunter if catching both pawya and grenwall. This all depends on the current Grand Exchange prices, average spikes per grenwall, and if herbs are collected or not. Refer to the grenwall page for more information about hunting them.
Grenwall spikes were reducing gradually in price due to bots flooding the hunting locations; going from an extremely profitable way to skill to much less profitable. When ClusterFlutterer was released the price started to rise again.
Later, completing the medium Tirannwn Tasks makes it possible to hunt grenwall without requiring to bait the traps, the hourly hunter experience became even more. As a result grenwall spikes became a lot more common, causing the prices to crash.
Furthermore, after the release of Ornate tortles the spikes started rising again due to the lower amount of high levelled players using them as a training method, instead opting for the higher xp/h tortles and as a result less spikes entering the game.