What is the need for parasites to develop special adaptations?

Some special adaptations developed by the parasites are:

• Some parasites have hooks, suckers, rostellum, etc., for anchoring. Example: Taenia solium
• Some intestinal parasites have enzyme resistant protective cuticle. Example: Ascaris
• Some parasites like Entamoeba develop cysts to overcome the unfavorable conditions.
• Some intestinal parasites produce anti-enzymes to neutralize the effects of hosts digestive enzymes. Example: Taenia solium
• Some parasites live as obligatory anaerobes. Example: Entamoeba
• While some parasites live as facultative anaerobes. Example: Ascaris