There are three main types of symbiotic relationships:

* Mutualism: Both species benefit from the interaction. For example, bees pollinate flowers while getting nectar.

* Commensalism: One species benefits, while the other is neither harmed nor helped. For example, barnacles attaching to whales get a place to live and food, but the whale is unaffected.

* Parasitism: One species benefits, while the other is harmed. For example, a tapeworm living in a human's intestines gets nutrients, but the human is harmed by the parasite.

So, while not all symbiotic relationships are beneficial to both species, they all involve at least one species gaining something from the interaction.