Infestation of Mayflies in Nee Soon South

Er Dr Lee Bee Wah asked the Minister for the Environment and Water Resources (a) what are the reasons for the infestation of mayflies at certain blocks of flats in Nee Soon South; (b) how can NEA help to put a stop to it; and (c) how long will the eradication measures take to produce tangible results.

Mayflies are a type of small flying insects that are found in freshwater streams, rivers and reservoirs. They are not vectors, that is, they neither bite nor transmit diseases. In fact, mayflies are universally recognised as indicators of good water quality. They are also key for a balanced ecosystem as they are food for a variety of animals who live in our reservoirs. Mayfly larvae can only live in clean and clear water and they emerge from the water when they are adults to mate for a very short period of time. While mayflies can be found in all our reservoirs, they have been particularly abundant in Lower Seletar Reservoir.

PUB receives a handful of feedback through the year – December-March and July-September – on the emergence of mayflies around the HDB blocks in Nee Soon South near Lower Seletar Reservoir. Their emergence is seasonal and lasts for a short period of time, about one to two weeks, as each adult can only live for a few days. While mayflies may be an occasional nuisance, they are harmless insects that occur naturally in areas around our reservoirs.

PUB has provided advice to residents who wish to take measures to prevent mayflies from entering their homes. These include switching off their lights when not in use as mayflies are attracted to light, installing insect screens at their windows or drawing their curtains, if needed. PUB has been carrying out regular checks around Lower Seletar Reservoir to monitor the counts of mayflies. Routine fogging for general pest control and mosquito control are carried out around the reservoir grounds and this routine fogging will also kill mayflies.

I would like to once again assure members and residents of Nee Soon South that mayflies are harmless insects and an essential part of our natural aquatic ecosystem. Therefore, we seek residents' understanding and tolerance, should they find these harmless mayflies in their homes.