The weather has become so unpleasantly cold that I try not to open my eyes while walking outside, out of fear that my eyeballs will freeze. (I was told that this would happen by my teacher in preschool; she also told me that eating candies makes worms lay eggs in my teeth, and that if I eat pears before swimming then I will drown. Why pears and not, let’s say, gooseberries, I have no idea, and I won’t even mention what she said would happen if I ran with scissors.) Anywho, the lifeless season outside the window makes me seek solace in memories of warmer places, luxuriantly abundant with life, and few phenomena better convey the feeling of life’s unbound exuberance than swarms of tropical butterflies.
Visitors to the tropics are often surprised by the number of butterflies and moths aggregating on muddy banks of rivers, mud puddles and, this usually comes as a surprise, animal dung. Many butterflies are also attracted to human skin and suck sweat or blood from cuts with their proboscis. They love wet, sweaty socks and shoes, and absolutely adore the stuff that seeps out latrines. We may delude ourselves that all butterflies prefer sweet nectar of flowers, but in fact many would rather gorge on the liquid portion of fresh feces.
This behavior, known as puddling, is decidedly more common among male than female butterflies. A series of studies has demonstrated that the main element these insects are after is sodium. Sodium is difficult to find in plant material consumed by the butterfly larvae, although potassium occurs there in abundance. By sucking fluids rich in sodium, adult butterflies try to replace the surplus of the latter element with the former. In extreme cases a moth may imbibe an amount of fluid 600 times its own weight in a single puddling session, expelling the excess water as it drinks and retaining only the precious mineral. It has been shown that a higher sodium content in the male’s body enhances his mating success i.e., fitness. In addition to sodium, moths and butterflies may extract amino acids from soil and animal excrements, and males of some species transfer these compounds to their partners through a spermatophore during mating, thus investing in their offspring.
While in Guyana a few years ago I noticed a particularly large aggregation of butterflies on the sandy bank of a small river that was lazily flowing near our camp. The patch of sand that the insects were obsessing about didn’t look any different from the rest of the beach, but there had to be something in it that made the butterflies go crazy. I had my suspicions as to what was in the sand, but decided to find out for sure. Alas, after many hours spent crawling around, watching and photographing the butterflies, the reason for their strange behavior was still a mystery. But the following night, as I quietly crept through the forest searching for katydids, I suddenly heard the unmistakable sound of water gushing from a faucet. As quietly as I could I moved closer to the river, and there it was – a huge tapir, taking a leak on the patch of sand where the butterflies loved to aggregate, and where I had just wallowed in for hours. My consolation is that the sodium and amino acids that I surely must have absorbed through my skin might increase my fitness as well.