Hi Dr. Kada,
Those are either Dragonfly Nymphs or Damselfly Nymphs... Very voracious larval stages of Dragonflies and Damselflies.
https://i.pinimg.com/originals/96/4d/af/964dafede12e2c0a08d74ef574ad601b.jpg69
See the mouth in the picture.. that thing will extend far beyond its eyes when it strikes to capture prey (e.g. mosquito larvae, fish, shrimp, tadpole, and etcetera)... lightning fast.
Kind regards,
Nelson