The Butterfly Labial Palps

The Butterfly Labial Palps

Labial Palps of the Butterfly - Its Olfactory Sensory System

The exceptionally hairy labial palps of a Common Three Ring

Every butterfly possesses labial palps (or palpi) - a pair of hairy, moustache-like scaly appendages on the head of the butterfly. These palps are covered with sensory hairs and are believed to help a butterfly "taste" food sources and identify what is potentially edible and what is not. The labial palps are multi-segmented external organs and vary in size and shape across the different families of butterflies.

There are also other theories that suggest that the labial palps of a butterfly serves other functions. For example, one theory suggests that the pair of palps, given their symmetrical location on both sides of the proboscis, could offer some form of physical protection for the proboscis. It would appear to be highly plausible in some species, where the proboscis is completely hidden by the labial palps until the proboscis is uncoiled for feeding. However, in other species, the size of the labial palps is not adequately large enough to cover even half of the coiled proboscis, leaving the proboscis exposed.

© Encyclopedia Britannica (left) and © NC State University (right)

Another suggestion of the function of the labial palps would be that the long hairs covering the palps act as some form of filters and protect the eyes from being contaminated as the butterfly feeds at flowers or when puddling. Again, the extent to which this may be true or not, varies from species to species, from the extremely hairy labial palps of a Satyrinae butterfly, to the smooth and more robust labial palps of some of the Nymphalidae.

In field observations, one can observe the movement of the labial palps when the butterfly uncoils its proboscis to feed. The muscles in the head of the butterfly appears to be able to control the antennae, proboscis and the labial palps independently but yet at the same time, coordinated enough to allow maximum efficiency for the butterfly to fulfil its primary objective to extract as much food source as possible when it feeds.

The physical appearance of the labial palps varies quite a bit across the different families of butterflies. In some cases, the palps are short and plump and held closely to the head of the butterfly. In other examples, the palps are extremely hairy, whilst some are stubby and smooth. Some species have the last segment of the palps modified and stick out like a pair of horns, and some examples show the palps sticking rigidly and extending beyond the head of the butterfly like a snout.

The labial palps of the Club Beak butterfly (Libythea sp.) gives it an appearance of  a face with a snout

A unique example of the labial palps evolving into something remarkable in a butterfly would be the "Club Beak Butterflies" or "Snout Butterflies". Although these species do not fly in Singapore, they are distinctive enough to be mentioned and shown here as an example of butterflies where the extended labial palps gives them an appearance of having a long snout.

The labial palps of the Papilionidae are compact with short hairs

Let us now take a look at this examples of this morphological feature across the different species in the families that can be found here in Singapore. Amongst the large Papilionidae, it can be observed that the labial palps of the majority of the species in this family are compact and held close to the head of the butterfly. The hairs of the labial palps sometimes take on the bright colours of the butterfly's body, like in the Common Rose.

The labial palps of the Common Rose takes on red hairs and gives it a distinct appearance

Given the long and thick proboscis of the Papilionidae and the comparatively compact labial palps, it is obvious that the palpi does not cover nor protect the proboscis at all, unlike some other butterfly species that we will see in the later part of this article. The sensory hairs on the labial palps are also short and thick and does not in any way extend out in front of the head of the butterfly.

In the next family, the Pieridae, the labial palps are also compact but are generally covered with longer and thicker hairs. Species from the subfamily Pierinae have labial palps covered with longer hairs and the last segment of the palps ends in a sharp point. Species from the subfamily Coliadinae, however, have compact labial palps and do not have the last segment ending in a point.

The large butterflies in the subfamily Danainae of the Nymphalidae family have compact and rather indistinct labial palps covered in short hairs. The last segment of the palps ends in a short stubby tip. The compact labial palps do not cover the proboscis completely when coiled - the proboscis is partially exposed and extends beyond the labial palps.




The labial palps of this Malay Baron gives it a beak-like look when viewed from the top


The Tawny Coster's labial palps are covered with yellow-coloured hairs

There is a wide variety of shapes of the labial palps of the several subfamilies of the Nymphalidae. Some are covered in sparse and fine hairs, like the Malay Lacewing, whilst others, like the butterflies of the Baron genus, have short stubby labial palps that look like a beak when the butterfly is viewed dorsally.



The genera Ypthima and Mycalesis features butterflies with exceptionally hairy labial palps, giving them an appearance of an unshaven face.

Of special mention are some species from the subfamily Satyrinae that feature exceptionally long hairs on their labial palps, giving the butterfly an appearance of an unshaven face. These long hairs on the palps completely hide the proboscis from view.



The Riodinidae butterflies have very compact labial palps with short hairs that can conceal their thin and short proboscis completely

The Riodinidae butterflies have very compact labial palps with very short hairs covering them. The palps are held tightly against the head and completely hide the short thin proboscis of the majority of the species in this family of butterflies.


The labial palps of this Curetis sp. are speckled with red spots

Amongst the Lycaenidae, the labial palps of many species have sharp distinct terminal segments protruding beyond the head. In some species, the extended labial palps give the butterfly an appearance of having a snout. Species from the Curetinae subfamily have red spots on the palps and are diagnostic features for separating the species in the group.


This Biggs' Brownwing has long labial palps that look like horns on the butterfly's head

Species from the Miletinae subfamily have long, smooth labial palps making the butterflies appear to have a second set of short horn-like antennae from its face. The thin proboscis is hidden between the labial palps.




Labial palps of various shapes and sizes amongst the Lycaenidae butterflies

Other species amongst the Blues and Hairstreaks have labial palps extending way beyond its compound eyes and is prominently featured like pointed horns sticking out from the butterfly's head. In several species, the labial palps are coloured distinctly.


The labial palps of this Yellow Banded Awl are broad and covered with short hairs. The terminal segments end in two needle-like appendages sticking out from the face of the butterfly

Finally, amongst the Hesperiidae, the labial palps of many of these robust-bodied species of butterflies are wide and covered with short thick hairs. The terminal segment of the labial palps of several species from the Coeliadinae subfamily end in a short, smooth needle-like points emerging from the head of the butterfly.


The thick and wide labial palps in skippers can almost hide its long proboscis

This Yellow Chequered Lancer extends its labial palps away from its face, making it appear strange

This newly-eclosed Orange Awlet extends and adjusts its labial palps (left) before retracting them close to its face (right) 

A unique behaviour amongst the Hesperiidae is that the butterfly can extend the labial palps beyond its face, pushing the palps forward in a remarkable fashion, making the face of the butterfly appear strange. In newly-eclosed individuals, this behaviour is also sometimes observed, as the butterfly extends its labial palps. In the majority of species of Hesperiidae, the wide and significant labial palps are able to almost totally conceal the coiled proboscis.



When you are out in the field next, do take a much closer look for this unique morphological feature in butterflies and share any special observations that you may have of the labial palps of butterflies.

Text by Khew SK : Photos by Khew SK, Bobby Mun and Nelson Ong

Butterfly of the Month - June 2018

Butterfly of the Month - June 2018
The Gram Blue (Euchrysops cnejus cnejus)


A Gram Blue feeding on the flower of the Coat Button (Tridax procumbens)

Today is the last day of June, and we are theoretically just right in the middle of the year, with the other half of 2018 starting from tomorrow. The warm summer is already in full swing in the northern hemisphere, with several countries reporting temperatures in the high 30's. I was in Beijing in third week of the month, and the temperature was unbearably hot, hitting 35degC to 38degC. Coupled with a Relative Humidity of 17%, it felt a lot hotter and drier when outdoors.




The temperature range this far north in China is quite amazing, when one considers that just six months ago, in December when I was there, it was a bone-chilling -4degC! What was interesting in Beijing, was that in the three days that I spent there, the air quality was surprisingly good.  Perhaps government intervention has finally reaped some positive results in terms of reducing the pollution in this capital city of China?





Any commentary on world news in the month of June surely cannot omit the historic summit between US President Donald Trump, and North Korean leader Kim Jong Un. For the first time, a sitting US President and a North Korean leader, representing two countries which have never seen eye to eye nor whose leaders ever met before, will meet face to face, and our little red dot island nation host this unprecedented meeting.


A mating pair of Gram Blues

With North Korea's denuclearisation on the cards, and primarily to avert a nuclear war in Asia, the stakes are high, as all eyes watched closely the meeting between two highly volatile and eccentric leaders. That the island nation of Singapore was chosen is testament to its efficiency, infrastructure and organisational competency.




Nevertheless, the government of Singapore and its agencies rose to the occasion and the summit went without a hitch - albeit with a negligible inconvenience to the routine lives of locals who went about their daily business. But the usual complaints and grouses were almost silenced, as most would understand the serious consequences should anything untoward happen to the summit as a result of organisational or logistical oversights!



What was amusing were the handful of 'wefies', courtesy of our own politicians - probably the first ever taken of Kim Jong Un, and then posted on social media. The North Korean security personnel stopped anyone close enough during Kim's evening walkabout in Singapore from taking photos of him, but were most likely caught unawares that Singapore's Ministers would be brazen enough to take wefies of their beloved President. No harm done, but another 'first' amongst firsts during this historical summit.




Closer to home, the new Malaysian government created certain surprises, one of which was the cancellation/deferment of the High Speed Rail system linking Kuala Lumpur and Singapore. Citing reasons of high costs and rising debt, Prime Minister Dr Mahathir's government reviewed several high-budget projects in Malaysia. He also raised 'long-buried' bilateral issues like the Pedra Branca islands and the supply of water to Singapore. Interesting times ahead for Singapore and our physically closest neighbour.



Back to our Butterfly of the Month for June 2018, we feature a relatively small and common species, the Gram Blue (Euchrysops cnejus cnejus). The Gram Blue is a widely distributed species, and is sometimes common in urban areas where its caterpillar host plants, Tropical Kudzu (Pueraria phaseoloides) and Creole Bean (Vigna reflexopilosa) can be found. These common creepers usually appear in recently cleared road verges and newly planted areas.




The Gram Blue is usually found fluttering restlessly amongst low shrubbery along roadside greenery on hot sunny days. Where it occurs, it can sometimes be even abundant, with up to a dozen individuals - both males and females, fluttering around and frolicking in the sun.



Male Gram Blue (top) and female Gram Blue (bottom) with open wings showing the upper surfaces of their wings

The male of the Gram Blue is light purple blue above, whilst the female is heavily black-dusted, with the wing bases a pale shining blue. The underside is pale buff, with the usual dark grey striations and spots. The two prominent black spots on the costal area on the underside of the hindwing is quite consistent in many lookalike species like the Cycad Blue, Forget-Me-Not and Silver Forget-Me-Not, creating a bit of confusion when these species are observed in the field.


Note the two orange-crowned black tornal spots on the hindwing and the short tails of the Gram Blue 

However, to distinguish the Gram Blue, look for the two orange-crowned black tornal spots on the underside of the hindwing. These spots are also edged with metallic green scaling. The tails of the Gram Blue are also shorter than its lookalike cousins and with these few diagnostic features, identifying the Gram Blue should be less of a challenge.


A Gram Blue feeding on the flower of its caterpillar host plant, Creole Bean (Vigna reflexopilosa)

At certain hours of the day, both the males and females of the Gram Blue may be seen opening their wings to sunbathe on leaves and blades of grasses in their usual habitats. Males also chase each other and when one is perched to rest, another individual may "attack" it and get it to fly off in an endless chase.



Gram Blues puddling

Males of the Gram Blue may also be observed to puddle at damp sandy footpaths and also decomposing organic matter. The caterpillars of the species are attended by ants, and the pupa attaches itself to the underside of leaves with a very thin silken girdle.

Text by Khew SK : Photos by Chng CK, Huang CJ, Khew SK, Michael Khor, Koh CH, Loke PF, Nelson Ong, Simon Sng, Jonathan Soong, Tan BJ and Anthony Wong