Water scorpion

The water scorpion (Nepa cinerea) is a member of the Nepidae family within the order Hemiptera. Despite its name, it is a aquatic bug that uses a snorkel-like siphon to breathe air while remaining submerged. It is commonly found in stagnant waters, ditches, and ponds across various temperate regions.

In the context of agricultural and aquacultural practices, it is considered a pest in nurseries and fish ponds. It is a sit-and-wait predator that prefers shallow water where it hides in the detritus or among dense aquatic vegetation to ambush its prey, including fish larvae and other beneficial invertebrates.

The biological cycle consists of incomplete metamorphosis. Females lay eggs inside the tissues of aquatic plants. The nymphs go through several molting stages, resembling miniature versions of the adults. These nymphs are equally voracious and contribute to the overall predatory pressure within the confined water environment.

The primary economic damage is linked to the loss of fish fry in breeding ponds. By feeding on the young fish, water scorpions cause significant depletion of stocks, leading to reduced yield in commercial aquaculture. Their presence is often overlooked until significant losses in the juvenile fish population are detected.

Effective control measures focus on habitat modification. This includes removing excessive aquatic weeds that provide hunting grounds and egg-laying sites. Managing the water level and using mechanical filtration can also help in reducing the population density of these predators, ensuring a safer environment for fish development.