noun
backswimmer (Notonecta triguttata)
A species of aquatic insect that swims on its back. The name is usually written in katakana.
池でマツモムシを見つけた。
I found a backswimmer in the pond.
The name マツモムシ literally means 'pine seaweed bug', likely from its habitat among aquatic plants. The exact derivation is uncertain.