It's called a mutualistic relationship! :)
I hope this helps!:)
Just to add on over time they have develiped a tuff outer layer to stop weather and insects from harming them.
Cinder cones derive their name from their steep sides, which give them a cone-like appearance. The angle of their slopes may be as steep as 35 degrees, although older, eroded cones have softer slopes. Cinder cones are small compared to other types of volcanoes. They average 100 to 400 meters in height (325 to 1,300 feet), while composite volcanoes may reach 3,500 meters (11,500 feet) and shield volcanoes can range as high as 8,500 meters (28,000 feet) -- the height of Hawaii's Mauna Loa, the world's largest, as measured from the ocean floor to its top. Most cinder cones are monogenetic, which means they erupt only once. Their eruptions tend to be relatively weak compared to those of larger volcanoes. Cinder cones often form as parasite cones along the flanks of larger volcanoes. They are formed by Strombolian eruptions, when gas forces steaming lava upwards into the air. The lava cools and falls to the earth as pebbles, which build up around the vent that ejected them, forming a cone. These parasite types of cone volcanoes usually occur in groups. Shifts in the position of the vent result in twin cinder cones. Variations in the power of eruption create nested cones. Not all cinder cones are found in groups; some are separate entities formed on basaltic lava fields.
