Life History of the Aberrant Oakblue

Life History of the Aberrant Oakblue (Arhopala abseus abseus)

Butterfly Biodata:
Genus: Arhopala Biosduval 1832
Species: abseus Hewitson 1862
Subspecies: abseus Hewitson 1862
Wingspan of Adult Butterfly: 28-30mm
Caterpillar Local Host Plants: Hopea pachycarpa (Dipterocarpaceae), Hopea odorata (Dipterocarpaceae).





Physical Description of Adult Butterfly:
The Aberrant Oakblue differs from other Arhopala spp. in having a short tail at the end of vein 3 of the hindwing, and a very short vein 9 in the forewing. Both features suggest that Aberrant Oakblue is more closely related to the Flos spp. than its placement in the Arhopala genus would otherwise suggest. Above, the male is deep violet blue with a dark forewing border expanding towards the apex (where it is about 4.0mm wide); the female is shining blue with broader borders. Below, the wings bear cryptic markings with most spots in blackish brown. Pristine specimens carry a strong purplish sheen in the discal area on the hindwing and white shadings in the forewing's apical and subapical areas. Most specimens feature a moderately large white spot at the mid-costal margin of the hindwing. Also on the hindwings, short white-tipped tails are found at the end of veins 1b and 3, and a moderately long white-tipped tail at the end of vein 2. The compound eyes are dark yellow brown.





Field Observations of Butterfly Behaviour:
In Singapore, the Aberrant Oakblue is not considered rare and adults can be found in the shaded forested areas within the nature reserves, Southern Ridges, Singapore Botanical Gardens and other wooded areas scattered across the island. They have a strong quick flight and are easily spooked by "overzealous" photographers. They typically rest in the shade among the foliage with upright wings.


Local host plant #1: Hopea pachycarpa.


Local host plant #2: Hopea odorata.

Early Stages:
Thus far it has been established that Hopea pachycarpa and H. odorata are utilized as larval food plants by the Aberrant Oakblue locally. Both plants are in the Dipterocarpaceae family, members of which are commonly utilized by butterfly species in the Arhopala and Flos genera. There are two other yet-to-be identified host plants in the local catchment reserves, both of which are likely to belong to this plant families as well. The early stages of the Aberrant Oakblue feed on the young tender leaves of the host plants, and often lives in the company of attending ants.


Two eggs of the Aberrant Oakblue.

Eggs are laid singly or in small groups of 2-5 on a young shoot or the underside of a leaf of the host plant. Each egg is about 0.8mm in diameter, white with a very light yellowish green tinge. It is shaped like a pressed bun with a slightly depressed micropylar area atop. The surface has a finely reticulated pattern of intersecting ridges and there are short sharp spikes at the intersections of these ridges.

Two empty egg shells of the Aberrant Oakblue.

It takes about 3 days for the egg to hatch. The newly hatched is pale yellowish in body color and has a length of about 1.3mm. It has a rather flattened woodlouse appearance with a large semicircular prothorax, a round anal plate, a yellowish brown head and long dorso-lateral and lateral setae. There are also a fair number of very short setae on the body surface. The newly hatched does not bother to devour the rest of the egg shell after its emergence.

Two views of a newly hatched caterpillar, length: 1.3mm.


Two views of 1st instar caterpillar, length: 1.9mm.

The 1st instar caterpillar feeds by skimming the surface of a young leaf, but later instars are able to consume the lamina in whole. Larval stages of the Aberrant Oakblue are gregarious and a few caterpillars have been observed in the field sharing a leaf shelter and adjacent feeding site with no animosity towards each other. As the 1st instar caterpillar grows, its body color becomes more yellowish green. A faint pinky red patch appears on the posterior abdominal segments. After about 2 days of growth, and reaching a length of about 2.5mm, the caterpillar moults to the next instar.

Two views of a 1st instar caterpillar, late in this stage, length: 2.2mm.

The 2nd instar caterpillar features long lateral hairs and a yellowish brown head. Long dorso-lateral setae are no longer present, but many very short setae appear on the entire body surface. A pair of faint dorso-lateral line runs along the length of the body. The prothorax is marked by a large yellowish brown patch. The dorsal nectary organ (DNO) is already visible on the 7th abdominal segment and highlighted with a small dark reddish patch stretching to the 8th segment. A rather large anal plate, black in color, dominates the remaining posterior segments. The pair of the tentacular organs (TOs) on the 8th abdominal segments are also distinguishable at this stage.


Two views of a 2nd instar caterpillar, newly moulted, length: 2.5mm.

Two views of a 2nd instar caterpillar, late in this stage, dormant prior to its next moult, length: 3.2mm.

The 2nd instar caterpillar has a functional DNO as ants living in its proximity are observed to actively attend to the young caterpillars, having been attracted to the nectary fluid excreted via the DNO. The ant-caterpillar association continues for all remaining larval stages of the Aberrant Oakblue. The 2nd instar caterpillar reaches a length of about 4mm, and after about 2-3 days in this stage, it moults again.

A late 2nd instar caterpillar (right) and a newly moulted 3rd instar caterpillar (left) of the Aberrant Oakblue.

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. New to this instar is a very large black prothoracic shield and a slightly smaller black anal plate. The DNO is now rather prominent with an dark brown oval ring marking its outer boundary. Faint dorsal and dorso-lateral bands are apparent at this stage too. The 3rd instar takes about 3 days to complete with the body length reaching about 6.5mm.

Two views of a 3rd instar caterpillar, newly moulted, length: 4mm.


Two views of a 3rd instar caterpillar, length: 4.9mm.

The 4th instar caterpillar has similar markings as the 3rd instar. One notable change is in the prothoracic dark patch which now has two small white patches embedded at its posterior, and one small white patch at its anterior edge. The dorsal and dorso-lateral bands are now more pronounced than in the previous instar. This penultimate istar takes about 4-5 days to complete with the body length reaching 10mm.

Two views of a 4th instar caterpillar, early in this stage, length: 7.3mm.


Two views of a 4th instar caterpillar, late in this stage, dormant prior to its moult, length: 9.5mm.

The 5th instar caterpillar has similar but more striking markings. Visible changes are 1) a white intermittent line running down the middle of the dark patch on the prothorax; 2) both the dark patch on the prothorax and the anal plate are now flanked by white borders. Another change is in the dark patch stretching from the DNO to the anal plate where there are two side-arms reaching and encircling the TOs on the 8th abdominal segment.


Two views of a 5th instar caterpillar, early in this stage, length: 12mm.


Two views of a 5th instar caterpillar, later in this stage, length: 17mm.

The 5th instar lasts for about 8-9 days and in the last three days of this period, the body of the caterpillar decolorises to a creamy white shade. It continues feeding in this form until the end of the instar.


Two late 5th instar caterpillar in white form, length: 18mm.

After reaching a length of about 18mm, the caterpillar slows down and stops food intake for about 1 day. During this time, its body length gradually shortened. Soon it becomes an immobile pre-pupa in its leaf shelter.

Two views of a pre-pupa of the Aberrant Oakblue in its shallow leaf shelter.

The pre-pupa caterpillar prepares for pupation by spinning a silk girdle and a silk pad to which it attaches via claspers at its posterior segments. After 1-1.5 day as a immobile pre-pupa, pupation takes place. The pupa, with a length of 11-12mm, has a shape typical of any Lycaenid species, but with a somewhat produced anal segment. It is creamy white in coloration. A small reddish-brown slit, likely the remnant of the DNO, has been found to exude fluid droplets for the first few days of the pupal period. This attracts the ants to attend to the pupa, thus securing some degree of protection from predators or parasitoids.

An Aberrant Oakblue caterpillar molts to become a pupa.

Two views of a pupa of the Aberrant Oakblue, length: 12mm.
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A sequence showing two caterpillars in various stages of pupation in adjacent sites on the same leaf.
Seven to eight days later, the pupa matures enough to show the shining blue patch on the forewing upperside. The next day, the pupal stage comes to an end with the emergence of the adult butterfly.

Two views of and instar caterpillar, early in this stage, length: 2.5mm.

A newly eclosed Aberrant Oakblue drying its wings near its empty pupal case.

Unlike most of the Lycaenidae species, the caterpillars of the Aberrant Oakblue have the habit of constructing leaf shelters in which they rest and seek safety between feeds on the lamina of nearby leaves and part of the shelter. Pupation also takes place within a leaf shelter.

Two views of a 3rd instar caterpillar of the Aberrant Oakblue receiving the attention of an ant.


A leaf shelter found in the field. Partly opened in the right panel to show the 5th instar caterpillar and attending ants.
Can you spot the caterpillar?

References:

• [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.
• Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006

Text by Horace Tan, Photos by Koh Cher Hern, Nelson Ong, Loke PF and Horace Tan

Lords of the Rings? - Singapore's Ypthima species

Lords of the Rings? - Singapore's Ypthima species

A casual reader of the Field Guide to the Butterflies of Singapore (2010) recently asked me, after looking through the pages of the Common ??? Rings. "They all look so similar and it's difficult to tell them apart. The number of rings on the wings also doesn't seem to match the English names! Why is that so?"

The Rings species, as we commonly refer to them, are relatively small and unattractive butterflies and tend to fly weakly amongst low shrubbery and grasses.  Two earlier articles in this Blog featured species from this genus, Ypthima- The Cinderella of Butterflies and Variability of the Common Four Ring.

This article sums up the five extant Ypthima species in Singapore, and provides an understanding of the subtle differences amongst the five, as well as shed some light on the naming convention used for their common English names.

The caterpillars of all the species of this genus comprise species of Graminae or generally, grasses.  The adults are greyish or pale buff brown, with striate undersides. All have a large subapical ocellus on the underside of the forewing, with a series of yellow-ringed black submarginal ocelli on the underside of the hindwing.

A Common Five Ring perches on a blade of grass

The basic ID Key to separate and distinguish the five extant species in Singapore is as follows :

Common Three Ring (Ypthima pandocus corticaria)
Underside hindwing with ocelli in spaces 1b, 2 and 6 only.

Common Four Ring (Ypthima huebneri)

Underside hindwing with ocelli in spaces 1b, 2, 3 and 6 ; but never an ocellus in space 5

Common Five Ring (Ypthima baldus newboldi)

Underside hindwing with ocelli in spaces 1b, 2, 3, 5 and 6.  The ocelli in space 5 is much larger than in space 6.  The ocellus in space 6 is sometimes missing, although there is not infrequently an additional small ocellus in space 4.

Malayan Five Ring (Ypthima horsfieldii humei)
Underside hindwing with ocelli in spaces 1b, 2, 3, 5 and 6.  The ocelli in space 5 and 6 are subequal, that in 5 sometimes smaller. Underside ground colour whiter.

Malayan Six Ring (Ypthima fasciata torone)
Underside hindwing with ocelli in spaces 1b, 2, 3, 4, 5 and 6.  All ocelli rather small and in an almost straight line. Underside of both wings are crossed by two dark and distinct fasciae.

English Naming convention

The curious naming convention in this genus is based on the number of rings (or ocelli) found only on the hindwing of the species.  In addition to that, the pair of rings, or what appears to be two rings encircled by a yellow outer ring at the tornal area of the hindwing in space 1b is counted as one ring instead of two. Hence in a species like Ypthima pandocus corticaria or what is commonly called the Common Three Ring, we can clearly see the number of rings on the hindwing of the species as shown in the photo below.

A Common Three Ring, showing the 3 ocelli on the hindwing

The members of the genus are highly variable, and aberrations are frequently observed. The two species with five rings - Common Five Ring and Malayan Five Ring, are particularly controversial, where their variability may be the subject of debate as to what constitutes one species or the other!

A Common Four Ring perches on a dead fern

In the earlier blog article on the Common Four Ring, this phenomenon is also exhibited, where the range of contiguity and size of the ocelli in spaces 2, 3 and 6 is also the subject of debate as to whether there are two distinct species, or just merely a variability in the arrangement and size of the hindwing ocelli.

The Common Three Ring (Ypthima pandocus corticaria)

This species is the largest in the genus found in Singapore. It is locally common in locations where its preferred host plant (a type of grass) is found.  It is more often found on the fringes of the nature reserves, but can occur in urban parks and gardens as well. 



The upperside is grayish brown with a large subapical ocelli on the forewing above.  The underside is heavily striated with three large ocelli on the hindwing, which gives it its English Common name based on the naming convention described above.

There are occasional individuals which display an additional small ocellus - sometimes contiguous, sometimes separated, from the large ocellus in space 6. Sightings of such individuals are rare, but the photos shown above and below (a mating pair of Common Three Rings) show two examples of such variations in the Common Three Ring.



The Common Four Ring (Ypthima huebneri)

The Common Four Ring is the smallest member of the genus, with four ocelli on the underside of the hindwing. Whilst the tornal ocellus is described as in line with those in spaces 2 and 3, these three ocelli are often very variable in contiguity and size as explained in the earlier blog article.

The species is relatively common, and can be found most frequently in urban parks and gardens, although their presence at the fringes of the nature reserves is also quite evident.

The Common Five Ring (Ypthima baldus newboldi)

Always smaller in size than the Common Three Ring, the Common Five Ring features ocelli in spaces 1b, 2, 3, 5 and 6 of the hindwing beneath.  Again, the variability of these physical characteristics bring about much debate about the species.  Whilst the hindwing ocelli in space 2 and 3 are "large and almost always contiguous", this characteristic appear to be not always reliable to identify this species. 

As if to confuse the matter even further, C&P4 records that "there is not infrequently an additional small ocellus in space 4!" This would effectively give the particular variant six rings instead of five!  An example of the Common Five Ring with six ocelli is shown below. 



In the mating pair shot below, it shows a clear difference in this characteristic between the male and female of the species in terms of the size and contiguity of the ocelli in spaces 5 and 6.  The mating pair also suggests that the two individuals are the same species, although displaying quite different ocelli characteristics.

The more often ID key that is used to identify this species, is the relative sizes of the two ocelli in spaces 5 and 6, in that the ocellus in space 5 is always larger than that in space 6, irrespective of whether they are contiguous or separated.

 

The Malayan Five Ring (Ypthima horsfieldii humei)

Appearing very similar to the Common Five Ring, the Malayan Five Ring's identification has frequently been the subject of debate. Sporting an arrangement of ocelli that is similar to its lookalike, this species also features ocelli in space 1b, 2, 3, 5 and 6 on the underside of the hindwing.

It has been described that the underside of the hindwing is whiter in appearance rather than the usual grayish buff, but in the field and with photos, the level of "whiteness" can often be misread due to lighting conditions.  However, in many individuals of this species, particularly males, the slightly darker postdiscal and submarginal fasciae are more distinct.

The most reliable ID characteristic thus far, would be to look at the ocelli in spaces 5 and 6. In the Malayan Five Ring, these two ocelli are usually similar in size, and more often, the ocelli in space 5 is smaller than the one in space 6.

The Malayan Six Ring (Ypthima fasciata torone)

This is the rarest member of the genus in Singapore.  It has been rarely seen, with the last few sightings around the northernmost extent of the nature reserves in Singapore.

Besides having a full complement of ocelli across the underside of the hindwing, stretching from space 1b to 6, forming a total of six rings, a distinctive feature of this species is the pair of dark straight fasciae crossing both wings.  The ocelli sizes can be variable, but are usually small and separated from each other, except for the pair at the tornal area.

This article compares the five species of the Ypthima in Singapore, and we hope that it has been helpful in aiding observers of the species of this genus to separate and identify them.

Text by Khew SK : Photos by Sunny Chir, Goh LC, Khew SK, Loke PF, Bobby Mun & Wong CM

References : [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.