also: つちぼたる
noun
Refers to the larval or larviform female of certain firefly species that live in soil and emit light. In Japanese, it often specifically means the larvae of the Genji or Heike fireflies, or the wingless female glowworm.
夏の夜、土手で土ボタルが光っていた。
On a summer night, glowworms were glowing on the embankment.
土ボタルは幼虫のまま光る。
Glowworms glow while still in their larval stage.
蛍 is the general term for firefly, including both adult flying fireflies and glowworms. 土ボタル specifically refers to the soil-dwelling, often wingless, glowing forms.
Compound of 土 (tsuchi, 'earth, soil') and ボタル (botaru, 'firefly'). The katakana portion is from 蛍 (hotaru), with rendaku voicing. The name describes firefly larvae or larviform females that live in the soil and glow.