water bug

US /ˈwɑː.t̬ɚ ˌbʌɡ/
UK /ˈwɑː.t̬ɚ ˌbʌɡ/
"water bug" picture
1.

タガメ, 水生昆虫

any of various insects that live in or on water, especially a large aquatic bug (family Belostomatidae) that can inflict a painful bite

:
I saw a large water bug swimming in the pond.
池で大きなタガメが泳いでいるのを見ました。
Some people confuse cockroaches with water bugs.
ゴキブリとタガメを混同する人もいます。