21 December 2019

Occasional Visitors

Occasional Visitors
Strays and Vagrants to Singapore

A Vagrant puddling with open wings

During the Northeast monsoon season in the region, the prevailing winds herald the wet season in Southeast Asia. The predominantly north-easterly winds blow from the South China sea towards Singapore bringing heavy rains and the occasional flash floods. The eastern coasts of West Malaysia and South Thailand are usually inundated with heavy rains during this period too.

The yellow arrows show the prevailing NE monsoon winds blowing from Malaysia towards Singapore

With the winds blowing from southern Johor towards Singapore, there have been observations in the past years that certain butterfly species that are not resident in Singapore suddenly appear during these months. Also, it is possible that some species are blown southwards in Singapore and somehow stay a little longer (if they are able to breed with available host plants).

This weekend's blogpost investigates some of these "strays or vagrants" that are typically not seen in Singapore. However, seasonally, they may appear for a short period of time, and then disappear as suddenly and may not be seen for several years thereafter. The list is not exhaustive and is just a sample of the "exotic" species that stray into Singapore from time to time.

1) The Wanderer (Pareronia valeria lutescens)

The Wanderer belongs to the Pieridae family, of which several species are known to participate in migratory behaviour. This species, in particular, the male, is a strong flyer and can likely bridge the sea gap between Johor and Singapore. With a little aid from the winds blowing in the right direction, it can likely reach the northern coasts of Singapore. The Wanderer has been spotted on the northern offshore island of Pulau Ubin. After several unconfirmed sightings, a lone female was successfully photographed in Feb 2011.

The males continued to be spotted from time to time, but taking a photo of the skittish and fast-flying male is easier said than done. The male Wanderer is pale blue above, with prominent black veins on both wings. In the female, the wings bases are yellowish with broadly black-dusted veins. When in flight, the upperside of the female closely resembles the Yellow Glassy Tiger. The underside is paler and the colours muted, almost resembling a weathered individual of a Yellow Glassy Tiger. The flight of the female closely mimics that of the distasteful Danaid, as compared to the speedy flight of the male Wanderer.

2) The Yellow Glassy Tiger (Parantica aspasia aspasia)

This slow-flying Danainae has been spotted many times all across Singapore - from Pulau Ubin in the north, to Gardens by the Bay in the south. It was also observed in the urban parks along the Southern Ridges. The species was once extant in Singapore, but is no longer considered a resident species of Singapore. It makes an appearance once in a while and is by no means as commonly seen as in Malaysia.

The Yellow Glassy Tiger, as earlier mentioned in this blogpost, is the model for the mimetic female Wanderer. Its wings are predominantly bluish-grey with narrow black longitudinal streaks. Each wing has a bright yellow basal patch of which the hindwing has a more extensive yellow area. Whilst it exhibits Batesian mimicry with the female Wanderer, it is also a classic example of Mullerian mimicry where the day-flying moth, Cyclosia pieridoides also mimics the Yellow Glassy Tiger for mutual protection via aposematic colouration.

3) The Orange Gull (Cephora iudith malaya)

Another Pieridae species, the Orange Gull was a very recent re-discovery on Pulau Ubin in Dec 2018. Reinforcing the theory that some of these Malaysian species appear in Singapore during the NE Monsoon months, the Orange Gull is one example. Again, with Pulau Ubin as the nearest pitstop to mainland Malaysia, it is likely that this is a wind-assisted stray that appeared in Singapore. Listed as extant in Singapore by the early authors, this species has not been reliably recorded for many decades until one year ago.

An Orange Gull spotted recently on Pulau Ubin in Singapore

The underside of the hindwing of the Orange Gull is yellow with the tornal area dark orange and brown marginal borders. On the upperside the wings are predominantly white with black veins but the tornal half of the hindwing is a bright yellow. The species is often observed puddling at sand banks with other butterflies. Like many of its related species in the family Pieridae, it is a strong flyer.

4) The Vagrant (Vagrans sinha sinha)

The Vagrant was another re-discovery when it was spotted by chance at Gardens by the Bay in June 2013. Though documented as a Singapore-extant species by the early authors, the Vagrant has not been seen on the island for several decades. It was then photographed again one year later, in June 2014 at the Seletar Golf Course Butterfly garden, and then again last year in Sep 2018 at a reservoir park. Whether there is a viable colony surviving on the island or not, remains to be seen.

The Vagrant is coloured a rich fulvous orange on the uppersides, with dark brown borders, spots and patches on both wings. The underside is paler, with light greenish scaling at the tornal area of the hindwing. It is skittish and swift in flight and can sometimes be found puddling. It has a characteristic half-open wing pose when foraging on the ground.

5) The Danaid Eggfly (Hypolimnas missippus missippus)

The Danaid Eggfly is one of three species of the genus Hypolimnas that are found in Singapore. One of the other species, Hypolimnas bolina, has two different subspecies flying here in Singapore. The Danaid Eggfly was recorded as extant in Singapore. However it is again, very rare and only a handful of sightings of the species have been made in Singapore. The majority of observations have been at the urban hill parks at the Southern Ridges.

The male of the Danaid Eggfly closely resembles the Great Eggfly and Jacintha Eggfly, whilst the female (which has not been photographed in Singapore yet), is a good mimic of the Plain Tiger (Danaus chrysippus chrysippus). On the underside the white hindwing patch is much larger than the related species, and there is a distinct costal marking on the hindwing that is a diagnostic characteristic of this species.

And there we have, 5 examples of strays or vagrants to the Singapore butterfly scene. It is likely that more will be seen in the coming years, as butterflies do not respect geographical or political borders and fly freely between adjacent countries.

Text by Khew SK : Photos by Khew SK, Koh CH, Loke PF, Bobby Mun, Nelson Ong and Michael Soh