It is not just the huge swallowtail moth Lyssa zampa that has been appearing in surprisingly large numbers here. A bumper crop of butterfly species has also been spotted this year.
Some species which have never been previously recorded here have made an appearance as well, and are believed to have flown in from across the Causeway.
Experts told My Paper that they have spotted at least five new butterfly species so far this year, compared with the usual two or three spotted yearly. The new species include the Lesser Albatross and the Red Spot Sawtooth.
They have been seen in Sime Forest near Venus Drive, Lower Kent Ridge Road and MacRitchie Reservoir. Most of them flew in over the last few months, starting from April.
Last month, many Singaporeans were reported to have seen the dark-coloured Lyssa zampa moth, which is nearly the size of a person's hand.
National University of Singapore (NUS) ecologist Anuj Jain said erratic weather conditions this year might have led to the rise in butterfly populations in Malaysia, causing more of these migratory species to fly here.
These butterfly species are usually found in the forest and can be found throughout peninsular Malaysia, including the Panti Forest in nearby Johor, he said.
"It's not a conscious migration," he said. "The unusual weather may have triggered a lot of plants to flower in Malaysia. Strong winds could have brought the butterflies here, too."
Butterfly expert Khew Sin Khoon said: "After months of bad drought followed by rain, the sudden growth of new leaves could have prompted butterflies to lay more eggs, contributing to the higher numbers of butterflies in Malaysia and Singapore."
The peak in numbers could also be due to the drop in the number of birds that prey on butterflies and caterpillars, because the avian migratory season has ended, said Mr Khew, who is an honorary research affiliate at the Lee Kong Chian Natural History Museum at NUS.
Likewise, local butterflies such as the Lemon Emigrant and Tailed Jay have been observed in greater numbers this year, due to the mass flowering, said Mr Anuj, who also heads the butterfly interest group at the Nature Society of Singapore.
Surveys are still ongoing to tabulate the number of local species observed this year, and the findings should be out by the end of the year, he added.
Butterfly enthusiast Gan Cheong Weei said that the naturalisation of new butterfly species here is an area that "warrants more studies".
The 51-year-old manager, who has been a butterfly watcher since he was a boy, said: "It's nice to have more of them here, but we don't know the impact that they will have on our local species."
Medical technologist Clayton Low spotted a Red Helen butterfly in Lower Kent Ridge Road a month ago. It is believed to have been spotted here for the first time and is almost as big as the Lyssa zampa, said the 30-year-old.
He added: "Hopefully, in time to come, many people will be aware that the number of species of butterflies we have is a good indicator of the biodiversity of plants we have here."
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