Dozens of Blue Tiger butterflies jostle for space on a few bruised leaves of rattlepod. Each square centimetre on these blackening, bleeding leaves is precious, enough for four claw-tipped legs and a proboscis. The claws scratch the leaf, the proboscis probes and sips poison.
Blue Tigers On Crotalaria. Photo by Rizwan Mithawala
The C-shaped scent pouches on the hind wings of the Blue Tigers give away their sex, and the purpose of their jostling. They are all males, and here for sap-sucking. The Rattlepod contains pyrrolizidine alkaloids, a kind of chemical compounds that many plants produce as defence against herbivores of all kinds. The compounds are infamous for liver and lung damage in cows and horses, and have also caused large-scale food-poisoning in humans. But for males of milkweed butterflies like Blue Tigers, the alkaloids are love potions: they help produce vital sex pheromones.
Most of the leaves have been half-nibbled by caterpillars of a moth, many of whom now peacefully nibble on the lower leaves, having possibly moved away when the boisterous winged brigade arrived, smelling alkaloids. The moth caterpillars, too, need the alkaloids for pheromones, and to make themselves toxic, and therefore unpalatable to predators.
The butterflies and the caterpillars, nibbling, scratching and sipping on the same plant, mostly mind their own business. Except, when the butterflies don’t. In a paper published last month in the journal Ecology, four naturalists report a bizarre observation from the coastal forests of the Tangkoko Batuangus Nature Reserve in North Sulawesi, Indonesia. It involves adults of seven species of milkweed butterfly, caterpillars of one of the seven species, and a lot of unsolicited scratching. Scratching leaves is all okay. But molesting your own kin?
“The larvae would contort their bodies rapidly in what appeared to be futile attempts to deter the persistent scratching of adults,” the authors of the paper write. They documented multiple adults, sometimes in mixed species groups, fervently scratching and sipping from the wounded and oozing caterpillars for hours. The harassers were so engrossed that they were oblivious to being touched by humans, the authors report.
Butterflies live secret lives. They are among the most studied insects on the planet, yet unbelievable dramas from their lives continue to unfold before the eyes and cameras that stalk them. Sometimes, butterfly behaviours unknown to science are documented by accident. The ‘adults scratching larvae for alkaloids’ were also documented unintentionally. Two of the four authors of the paper share a passion for butterfly photography. In December 2019, they decided to spend a holiday in the reserve doing just that. On the first day, they came across hundreds of milkweed butterflies, of several species, swarming around a specific patch of vegetation. The pursuit of butterflies, through the camera viewfinder, can dissolve one’s notions of time. The duo spent hours photographing the jostling butterflies. Going through the pictures at the end of the day, they realised they had chanced upon unusual behaviour. They spent the next few days photographing butterflies repeatedly visiting the same wounded caterpillars, and scratching and sipping from them. The butterflies also imbibed from dead caterpillars, though the authors could not determine whether the deaths were due to the harassment by the adults.
In all likelihood, these are the first reported observations of milkweed butterflies imbibing from live caterpillars, rather than plants or carcasses of other insects. The authors have presumed that alkaloids are transferred from the bodies of the caterpillars to the adults, but it is yet to be proved chemically. Yet, since the behaviour is new to science, the authors have coined a term for it: kleptopharmacophagy, consuming stolen chemicals for non-nutritive benefits.
On a stroll in a Mumbai garden in early 2012, I photographed a Tawny Coster butterfly laying over eighty eggs on the underside of the leaves of a shrub unknown to me. I also photographed its caterpillars feeding on the same plant. After getting the plant identified as Turnera ulmifolia, commonly called yellow alder, and looking it up on the internet, I realised that it was reported as a new larval host plant of Tawny Coster in the May-Aug 2011 issue of Journal of the Bombay Natural History Society. I had missed publishing the record myself by merely a few months.
On many other occasions, I have photographed butterflies doing strange things, and have had to show the pictures to senior naturalists to figure out what behaviour or ecological interaction I have photographed. Yet, there are a couple of photo sets wherein the behaviour documented remains a mystery. Those pictures sit in my hard drive, and tantalise me every time I look at them, with the distant promise of a scientific paper that will reveal yet another butterfly quirk, and bewilder butterfly buffs.
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About the author: Rizwan Mithawala is a Conservation Writer with the Wildlife Conservation Trust and a Fellow of the International League of Conservation Writers. He has previously worked as an environment journalist with a national newspaper.
Disclaimer: The author is associated with Wildlife Conservation Trust. The views and opinions expressed in the article are his own and do not necessarily reflect the views and opinions of Wildlife Conservation Trust.
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