Butterflies fly from one plant to the next for food. They feed on tree-sap, nectar, nutrient-rich stream waters, fluids of rotten fruits or animal scats.
Butterflies play vital roles in the food cycle. They are the prey of birds, lizards, and amphibians. In fact, butterflies are the telltale signs of the health of any given ecosystem. And, Bangladesh has a staggering number of these biological good omens.
Butterflies are globally distributed except for the snow-capped Antarctica. About one-fourth of about 19,000 species of butterfly live in the Australasian region.
How many live in Bangladesh? Torben B Larsen, a Danish insect specialist with years of work on the Indian and African butterflies, predicted about half a thousand species.
The butterfly specialists of Bangladesh are very close to reaching Larsen's mark. More than 400 species have already been recorded in Bangladesh. The mixed evergreen forests of Sylhet and Chattogram are the treasure trove of butterfly diversity.
Into the secret lives
The butterflies we see are all adults. As with other insects, butterflies follow a life cycle. From egg to a wiggly larval form to an inert, dead-looking pupa to the final butterfly form—they have four stages in their life.
Each butterfly has one or two plants intertwined with their lives. Some butterflies are completely dependent on just one plant species. Others use a range of plants, often members of a common plant family.
Hence, the butterfly diversity and abundance in any given location are highly dependent on the availability and abundance of the specific host plants. These plants are known as host-specific plants as they host particular butterflies.
Single to several dozen eggs are laid on the host plant's twigs by female butterflies. The egg stage may last from a few days to a few weeks. Larvae come out of eggs and feed on the leaves of the plant.
The fully-grown larvae stop feeding, and, in a secure site – often the underside of a leaf--it wraps itself around a hardened shell called chrysalis. Within this, they undergo massive changes until an adult butterfly emerges in one fine sunny morning.
Butterflies can live from a week to nearly a year. Many species have long larval life stages while others can remain dormant in their pupal or egg stages that can go for an entire winter.
Without the plants, there will be no butterflies. How many greens have we spared in our cities?
Flying solar panel
Wings of the butterflies are not only for decorations and fluttering flights. The vibrant wing colours can guarantee successful pair bonds and deceive the predator by mimicking.
Butterfly wings can also transform energy. The wings are primarily made of millions of membranes and pigmented nano scales. These scales form a complex cellular network of a solar panel to absorb heat from the sunlight while basking.
The heat then transforms into energy and passes through the wing veins to thorax for flighting, says the 2017 study carried out by Dr Radwanul Hasan Siddique, a former Bangladesh University of Engineering and Technology (BUET) graduate and now a leading scientist of metaphotonics.
Like birds, fishes, dolphins, and turtles, many butterflies can migrate for a long distance. Butterflies navigate using the sun as compass and maintain their routes through chemical cues.
However, unlike birds, butterflies move in generations. No single individual completes the whole trip, rather, they breed through the journey. A set of generations complete the round-trip.
For example, monarchs are likely the most-studied among butterflies for long flights and cyclic journeys. They travel thousands of miles, covering the entire lower half of North America all the way down to Mexico.
The British painted lady, a Euro-African species, undertakes a 9,000-mile round trip in a series of steps. A single migration requires six successive generations from tropical Africa to the Arctic Circle--almost double the length of the monarch migration.
Migration of the Indian butterflies is monsoon specific, usually beginning in October from plains to South India. The return journey starts in April.
Butterfly migration is not studied much in Bangladesh, although we know we have some local and trans-boundary migrant butterflies: the painted lady, lime swallowtails, emigrants and tiger butterflies, etc.
The smallest, the largest, and the endemic
The Oriental grass jewel is the smallest butterfly of Bangladesh. This is a kind of small lycaenid or blue butterfly. Its wingspan ranges from 20 to 22 millimetres. The first observation of this species came from Dhaka. In 2014, the species was found from the bushes of sand-filled wetlands of Keraniganj. Recently, it was, again, photographed from the riverine sandbars of Rajshahi.
The golden birdwing is the largest butterfly species in Bangladesh with the wingspan ranging from 119 to 188 millimetres. This is a type of swallowtail found only in hilly forest of eastern region. At the first look, it might look like a small yellow bird with black wing flying high up in the sky.
The Sundarban crow, a Critically Endangered butterfly found only in the Katka and Kochikhali grasslands, has been only recorded, so far, in Bangladesh Sundarbans. Hence, it is dubbed as the only species of the country that is found nowhere else on this planet.
How threatened are our butterflies?
Bangladeshi butterflies are less explored. The 2015 threat assessment of the country's butterflies listed 305 species. About 62% of species were included as species threatened with extinction. Later on, many insect specialists and enthusiasts found the list incomplete, suggesting a revision of the assessment itself.
These issues reflect a limited understanding of the country's butterfly diversity, distributions, and population trends. A superficial, undermined species diversity can seriously deprioritise conservation efforts for butterflies as well as the forests that harbour them.
True that the direct loss of natural forests combined with the disappearing native host plants, drying up stream beds, use of insecticides, pesticides, conversion of forest ecosystems put butterflies at risk. But these threats had not been considered in the assessment.
And, we need to have a thorough survey first to mark out the butterfly hotspots.
Butterfly watching: a hobby and beyond
Watching and photographing butterflies has become a popular hobby. In Bangladesh, butterflies are commonly seen in all areas and even the urban parks and botanical gardens of Dhaka city. Urban greeneries reveal a significant diversity of over 140 species of butterflies, promoting the growth of a butterfly-loving community.
Public universities such as Jahangirnagar University and NGOs like International Union for Conservation of Nature (IUCN) Bangladesh arrange butterfly fairs every year. This national event encourages butterfly watching, research, and conservation.
Butterfly Young Enthusiast is the prestigious award offered by the fair yearly to the exceptional butterfly discoveries and researches. For example, a team from Jagannath University discovered over two dozen new butterflies for Bangladesh. The team lead earned the first award in 2014.
Butterfly watching at weekends is now a regular practice. "Butterfly Bangladesh", a Facebook group initiated by Shabu Anowar – a citizen scientist – now holds about 12,000 members. It serves as a common platform for butterfly-watchers, researchers, students and butterfly-lovers from various backgrounds.
Just in a decade since its formation, over 50 butterflies have been identified in this group that turned out new to the country checklist. Sharing rare butterfly photos in such social media sites is regarded as somewhat prestigious and appealing. Thus, distribution and occurrence of so many poorly known species are now well explored. These data are also vital in scientific research.
Taking care of the butterflies of Bangladesh can thus be a breather for our ecosystems, a decisive tool in our ongoing conservation efforts.
Butterfly wings can act as solar panels.
Butterflies are ecological indicators.
They are entirely dependent on specific host plant species.
Butterflies can fly for a 9000-miles trip.
The Sundarban crow, a Critically Endangered butterfly, occurs only in Bangladesh.
Two newly sighted butterflies
Dark Clouded Yellow, a butterfly new for Bangladesh, was recorded by some undergrad zoology students of Dhaka University in June this year.
Straight Pierrot Butterfly was sighted for the first time ever in Bangladesh during an expedition in Kassalang Reserve Forest last month. The expedition was jointly organised by IUCN Bangladesh and Bangladesh Forest Department to carry out a feasibility study for a transboundary wildlife corridor.