Testacella

Testacella is a unique genus of predatory terrestrial mollusks characterized by a small, rudimentary shell located at the posterior end of the body. Their elongated bodies reach 8–12 cm and are typically gray or yellowish in color.

Unlike common slugs, they lead a cryptic, subterranean lifestyle, spending most of their time underground. They possess powerful, specialized jaws adapted for capturing and consuming prey, including earthworms and other small gastropods.

Systematically, this organism belongs to the order Pulmonata and the family Testacellidae. The species most commonly found in Europe is Testacella haliotidea.

Visually, this pest resembles a common slug but is distinguished by its small "shield" shell and highly specific behavior. They rarely appear on the soil surface during the day, preferring nocturnal activity.

Their sensory organs enable them to actively track prey through soil burrows. This makes them not only potential garden pests but also active predators within the garden ecosystem.

Although Testacella is primarily a predator, it may damage underground plant parts when natural protein sources are scarce. Root crops, potato tubers, and young bulb shoots are at risk.

The primary damage involves burrowing deep into plant tissues, which provides entry points for infections. Bacterial rots and fungal diseases quickly develop within these wounds, often resulting in crop loss.

Both adults and juveniles living in the soil profile cause damage. Crops grown in greenhouses with high humidity are most frequently attacked due to the favorable environment.

Damage often goes unnoticed until harvest, as the mollusk consumes the interior, leaving the outer skin of the plant largely intact.

The severity of damage increases in years with rainy summers and warm autumns. Under such conditions, the mollusk population increases rapidly, leading to widespread damage to root systems.

The period of greatest activity for these mollusks is during the spring and autumn seasons. They prefer moist soil with temperatures ranging from 10°C to 20°C.

Reproduction occurs within the soil, where they lay their eggs. The complete life cycle depends on climatic conditions but typically spans one to two years until maturity.

Testacella hibernates in deep soil layers, below the frost line. With the first spring thaws, the mollusks begin migrating toward surface layers in search of food.

Peak activity is observed during prolonged rainy periods when the soil softens, facilitating movement within the ground.

Summer heat and drought force them into deeper soil layers to enter a state of dormancy. This protects them from desiccation but temporarily reduces their feeding activity.

The main sign of their presence is the existence of burrows in the soil, resembling earthworm tunnels but with a larger diameter. Plants may suddenly wilt despite adequate watering.

When harvesting root crops, one may find specific circular holes leading deep into the tissue. The interior of the root crop might be partially consumed or turned into a mushy state.

Presence of slime trails on the soil surface near plants is another indicator of nocturnal activity. However, due to their subterranean habits, observing the mollusks themselves is quite difficult.

Yellowing leaves on young seedlings, caused by root system damage, may also indirectly indicate the activity of subterranean mollusks.

In cases of heavy infestation, seedling death in entire patches may occur, which is often misidentified as wireworm or mole cricket damage.

The primary method of control is agronomic practice aimed at disrupting the pest's living conditions. Regular soil cultivation destroys the burrows and reduces their overall population.

The use of iron phosphate-based baits is considered the safest and most environmentally friendly control method. These pellets are applied in areas where pest activity is suspected.

Trapping, such as using containers buried level with the soil surface filled with beer or fermented juice, allows for the collection of active individuals at night.

Creating physical barriers made of wood ash, lime, or gravel around garden beds can hinder the movement of mollusks across the soil surface.

• Deep autumn soil tilling.
• Removal of plant debris and organic waste.
• Timely weeding to minimize shelters.
• Encouraging natural predators: hedgehogs, toads, and birds.