The correct option is
B An insect
Glowworm is the common name of groups of various insect larvae that show bioluminescence. This group includes various larvae of the families including Elateridae, Lampyridae, Phengodidae, and Rhagophthalmidae among beetles and also some members of genera Arachnocampa, Keroplatus, and Orfelia among keroplatid fungus gnats.
So, the correct answer is 'An insect'.