Bug of the Week continues its escape from our mild La Niña winter in Maryland and travels to Costa Rica where we previously met spooky amblypygids, colossal katydids, wary paper wasps, and friendly tarantulas. This week we meet beautiful Marpesia butterflies, the namesake of the fierce and beautiful warrior Marpesia, queen of the amazons. On a stretch of shoreline on the Osa peninsula, gorgeous Marpesia daggerwing butterflies gather on the beach to engage in a poorly understood behavior called “pumping.” No, this is not the kind of pumping Arnold Schwarzenegger or Hans and Franz made famous with heavy weights and muscular contortions. In previous episodes we met temperate swallowtail butterflies feeding on unusual substrates, including carcasses of fish and piles of dung, to obtain vital minerals and nutrients not found in nectar of more traditional hosts like the blossoms of flowers.
Watch as the lovely Marpesia sips from the sand and expels water from its abdomen about once every five seconds.
Butterflies frequently “puddle” in muddy soil using their proboscis to gather dissolved elements from moist mineral laden earth. “Pumping” is different. This infrequently observed behavior occurs when a butterfly rapidly imbibes water with its soda-straw-like mouthparts and rapidly expels it from the rear end. In 1963 Walfried Reinthal made the following observations of a swallowtail butterfly pumping at the edge of a swimming pool: “This pumping in of the water through the proboscis and at the same time eliminating it from intestines went on uninterruptedly for about the next twenty minutes. During this interim over two hundred and fifty drops of water were counted …” At a loss to fully explain this behavior Reinthal suggested that perhaps “the insect had to give itself a sort of internal lavage...” Other observations of pumping include those of Eduardo Welling who witnessed a swarm of about 30 swallowtail butterflies pumping in a “stinking hollow of mud” near a lagoon in Quintana Roo. He wondered if the behavior was related to the excessive heat and humidity of the tropical day.
Butterflies have many mechanisms to warm and cool themselves, the business of thermoregulation. Basking in the sun, avoiding conductive heat loss in the wind, and shivering are all used by butterflies to warm themselves. Respiratory cooling by evaporation and shade seeking are mechanisms used by butterflies to chill out on a hot day. In his treatise on thermoregulation in butterflies, Harry Clench suggested that pumping might be a way for a butterfly to rapidly warm or cool itself depending on the differential between ambient air temperature and the temperature of the water being pumped from the soil. Although I find the notion of butterflies performing self-lavage odd and intriguing, hey, in the world of insects stranger things have happened. Watching beautiful Marpisia pumping water on the beach is a phenomenal site to behold irrespective of the reason.
Bug of the Week gives special thanks to Carlos and the other rainforest adventurers at Aguila de Osa who were the inspiration for this episode. The articles "Behavioral thermoregulation in butterflies" by Harry Clench, "About the 'pumping action' of Papilio at water" by Walfried Reinthal, and "More observations of the 'pumping' action of moths at water, with notes on observations in Quintana Roo" by Eduardo Welling, were consulted in preparation of this episode.