Complex sentence: Large Blue caterpillars feed on wild Thyme or Marjoram flowers for the first few instars of development, and will then actively seek out the nests of Myrmica sabuleti, a specific species of red ant and hibernate inside their tunnels.
Split into simpler sentences: Large Blue caterpillars feed on wild Thyme or Marjoram flowers for the first few days of development. Afterwards, they seek out the nests of Myrmica sabuleti, a specific species of red ant, and hibernate inside their tunnels.