Living in the wild can be hard．Finding food and staying safe aren't easy．Each day, animals try to survive in their habitats．Not all animals get by on their own. Some animals form a close partnership with other kinds of animals．These pairings are called symbiotic(共生的)relationships．In a symbiotic relationship, the animals depend on each other．One animal helps the other meet its needs．Sounds good, right? Not always．Some animals are not very kind to their partners．In some cases, one animal meets its needs but hurts its partner．Take ticks(扁虱), for example．These insec