Water scorpion

The water scorpion (genus Nepa) belongs to the order Hemiptera and the family Nepidae. Despite their common name, they are aquatic true bugs known for their distinct morphology, including raptorial front legs and a long terminal breathing siphon that allows them to remain submerged while drawing air from the surface.

In an agricultural and aquaculture context, the water scorpion is considered a nuisance or a secondary pest. They do not feed on terrestrial crops, but they pose a significant threat to freshwater fish farms, particularly in hatcheries where they prey heavily on fish fry and small aquatic invertebrates.

The biological cycle of Nepa involves incomplete metamorphosis. Adults overwinter in debris or mud at the bottom of ponds. In the spring, they emerge to mate, and females deposit eggs into the tissues of aquatic plants. The nymphs develop through several stages, gradually acquiring the characteristics of adults while remaining in the aquatic environment.

The damage caused by water scorpions is strictly predatory. They are ambush predators that rely on camouflage to seize passing prey. In fish farming, their presence can significantly reduce the survival rate of young fish, leading to economic losses and requiring active population management to maintain high output.

Effective mitigation strategies for controlling water scorpion populations in managed aquatic systems include:

• Physical maintenance of ponds, such as removing excess vegetation to eliminate egg-laying sites.
• Seasonal draining and drying of ponds to eradicate overwintering populations.
• Introduction of biological controls, specifically fish species that naturally feed on aquatic bugs, provided they do not conflict with the primary commercial species.