They are called gravitraps, and are meant to help fight the spread of dengue by trapping female mosquitos.
But the placement of the traps along the corridors of some HDB flats has worried at least one resident.
When Mr Omar Haron, a 54-year-old private driver who lives at Woodlands Avenue 1, saw one of these traps outside his flat, he was concerned that it would attract more mosquitos to his flat.
"They ask us not to have stagnant water around our homes, but then they put stagnant water outside our homes to attract mosquitoes?" he said.
"I understand that the traps are to attract the mosquitoes to lay eggs and trap them with the glue inside, but before the mosquito lays eggs, it needs to suck someone's blood, right? That someone might be my family members or me."
The gravitrap is a container with hay-infused water to attract female Aedes mosquitoes looking for a spot to lay eggs. There is a filter to prevent them from laying eggs in the water and a layer of adhesive to trap them.
Mr Omar said he called the National Environment Agency (NEA) a few days after the traps were set, and they were removed the next day. But he thinks only the one outside his flat was removed because of his complaint.
"I think there was only one on my floor. But NEA told me that there were 90 blocks involved in the trial. So there must be many gravitraps out there," he said.
An NEA spokesman said that gravitraps are designed to attract Aedes female mosquitoes that are looking for sites to lay eggs, rather than those seeking humans to bite.
The traps are usually placed in areas that are attractive to the mosquitoes and reduce their population by trapping adult female mosquitoes and their eggs.
By tracking which traps are capturing mosquitoes, NEA can find out which areas have higher mosquito populations and are possible sources of mosquito breeding. This optimises its control efforts.
It was reported last month that NEA tested 1,300 gravitraps in Clementi and Bukit Panjang, and that the trials would be rolled out to other housing estates.
NEA also said that residents were informed of the placement of the gravitrap and its purpose before deployment. Officers check and maintain the gravitraps regularly to ensure that they are functioning properly.
In the week ending April 12, there were 247 dengue cases reported, seven cases more than the previous week.
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This article was published on April 19 in The New Paper.
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