A butterfly flapping its wings in South America can affect the weather in Central Park, the famous example for Edward Lorenz’s Butterfly Effect, the concept that small causes can have great effect. Though the headline bears resemblance, this is not a long winding article on meteorology and differential equations. It’s about literally butterflies and climate change.
The Butterfly Fauna of Sri Lanka by Dr. George Michael van der Poorten and wife Nancy E van der Poorten has just been published and will be available in Sri Lanka around mid May. It’s based on field research conducted over the past decade, as well as the personal experiences of the first author over the past five decades. The lives of all 247 species of butterflies in Sri Lanka are described and discussed in the book in detail.
Nation visited Dr. van der Poorten’s Hammaliya Estate, his private estate off Wariyapola that boasts of a butterfly garden that has recorded 125 species, to talk about climate change and butterflies.
“Butterflies are very sensitive to climate factors such as rainfall and temperature, but very difficult to use as an indicator species of climate change,” said Dr. van der Poorten. “Because they are also very habitat sensitive and the biggest threat to butterfly habitat is anthropogenic.” In layman’s terms their biggest threat is humans not climate.
Dr. van der Poorten explained that if temperature rises some species may stay and die off while certain species may move up in altitude in search of colder climate conditions. “But butterflies are adapted to a very specific regime and if the egg laying plants and food plants the particular species requires does not exist at this altitude the species may still die off.”
When asked if the food or larval host plants are affected by climate change, Dr. van der Poorten concurred. “Climate change effect on butterflies is two-fold; species die due to direct impact of climate change or it may die off due to lack of resources such as food and larval host plants that die off due to climate change.”
For example Spot Swordtail feeds only on a plant found in the Eastern part of Sri Lanka, Miliusa tomentosa, and consequently the Spot Swordtail population is also relegated to the Eastern part of the country. Similarly the Banded Peacock lays its eggs on Satinwood. “If Satinwood becomes scarce the Banded Peacock population will also decline.”
As we all know Satinwood is heavily logged. But logging is only one threat in the long list of threats to butterflies, identified in van der Poortens ‘ The Butterfly Fauna of Sri Lanka. Extensive use of herbicide and insecticide in agricultural production, industrial processes, habitat destruction to make way for residential areas and invasive species are a few major threats to these delicate fluttering fairies.
Extensive use of herbicide kills off larval host plants and food plants, while insecticide poses direct threat to larvae. A total of 12 invasive species that poses threat to butterflies by ousting their larval host plants and food plants have been listed in the book, Clidemia hirta of Sinharaja and Prosopis juliflora of Mannar to name a few. Two new species for Sri Lanka have been identified in the book; namely Orange Migrant and the Yellow Palm Dart.
“The focus of the book is not identification of butterflies, although it can be used for this purpose as well,” said Dr. van der Poorten. He explained that the focus of the book is how butterflies live. It contains vital information such as what strategies caterpillars use to evade predators. “For example adult butterflies of certain species mimic other poisonous butterflies to evade predators.”
The story of the Wood apple Blue is particularly interesting. The caterpillar of the Wood apple Blue eats its way into the wood apple. The plant knowing that it’s under attack tries to repel the imposter by oozing resin. The caterpillar pushes the resin out. Ultimately, knowing that the fruit is infested, the tree attempts to shed the fruit from the stalk. Knowing that it’s about to be evicted the Wood apple Blue caterpillar webs the fruit to the stalk, thereby preventing to from being shed.
It also discusses the origin of Sri Lankan butterflies and has dedicated 300 pages to each species. The book also traces migration patterns and mating habits of butterflies. According to Dr. van der Poorten, some butterflies are fond of fermenting material such as rotting fruits and believe it or not bird droppings and urine.
“Butterflies are very picky about where they lay their eggs,” explained Dr. van der Poorten. According to him, butterflies have very specialized requirements and if these conditions are not met, they disappear. The Butterfly Fauna of Sri Lanka contains a whole list of species and larval host plants and food plants.
The book is peppered with interesting butterfly trivia. For example some male butterflies sport a gland, referred to as the sex brand on their underside. This emits pheromones. “Certain plants emit smell that only a certain butterfly species is attracted to,” explained Dr. van der Poorten.
This explains why certain butterflies are attracted to only certain food plants. The more the adults feed on the nectar of these plants, the more smell they acquire,” explained Dr. van der Poorten.
“Some butterflies have what’s called scent pouches on the underside of their wings,” he explained, quite animatedly. “And when the male butterfly spies a female, it goes ‘Oh there’s a female, better make some scent, and dips it’s hair-pencils, a brush like contraption, into the scent pouches, takes them out and does a flyby extruding the hair-pencils and dispersing the scent, which is actually an aphrodisiac.” If the female likes the scent, well…then the male gets lucky.