These creatures are the main units of the Zerg ground forces.These units has very high artifical intelligence and their efficiency is so high.They are also adaptive to any type of attack.They can attack both air and ground in the same amount of damage points.They are suitable for drops (with overlords).They also can be converted into lurkers which are really superior against enemy ground armies.But if the enemy preperad a Hydralisk attack he can eridicate your forces by use of special units like Hightemplars/Tanks/Terran micro army(marine medic) or outnumbered mutalisk swarms.But except from these units, the hydralisk armies will be succesful at fighting.