Studies on the ecology of Bulinus globosus snails: Evidence against burrowing into the soil during the dry season

Abstract

Background: Bulinus globosus snail was the intermediate host of schistosome hematobium and hard to be found during the dry season. This study aimed to understand the vertical distribution of B. globosus in desiccated and re-hydrated soils and provide evidence on whether snails can drill into the soil for summer. Methods: Four laboratory/field experiments were designed to study the downward movement of the snails in desiccated soils or upward movement in re-watered soils. In Experiment 1, aquaria containing snails on the soil surface were placed in an outdoor environment to desiccate naturally. Then, snails were retrieved from different soil layers. In Experiment 2, snails on the soil surface were covered with an extra 5 cm layer of soil and 4 cm layer of water. The snail positions and survival rates were checked on the first, third, fifth, seventh, and ninth day. In Experiment 3, a seasonal ditch was selected in the field. After the soil in the ditch was naturally desiccated, 1cm, 1–3cm, 3–5cm, and 5–10 cm depth of soil layers were screened to retrieve snails. In Experiment 4, after the above ditch was naturally re-watered, snails were checked in the surface water once a week for 5 weeks. Results: At the end of Experiment 1, all the snails were only found at the soil surface. At the end of Experiment 2, snails were found neither within nor on top of the 4 cm layer of extra mud. At the end of Experiment 3, 96.92% of snails remained on the soil surface. Next, 2.77% of living snails were found in the mud crack within 1–5 cm depth. In Experiment 4, after the experimental field was naturally re-watered, no snails were found above the soil surface. Conclusion: B. globosus snails do not initially move downward into the soil during the dry season or upward to the soil surface after being re-watered.