Archive | January 2013

What butterflies like

In Eastern Cape of South Africa, a beautiful flock of butterflies is puddling on the side of a road. [Canon 7D, Canon 16-35mm]

In Eastern Cape of South Africa, a beautiful flock of butterflies is puddling on the side of a road. [Canon 7D, Canon 16-35mm]

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.

A cluster of puddling butterflies on a sandy river bank in Guyana [Canon 5D, Canon 100-400mm]

A cluster of puddling butterflies on a sandy river bank in Guyana [Canon 5D, Canon 100-400mm]

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.

African veined white (Belenois gidica) extracting minerals from wet sand (Eastern Cape, S. Africa) [Canon 7D, Canon 100mm macro]

African veined white (Belenois gidica) extracting minerals from wet sand (Eastern Cape, S. Africa) [Canon 7D, Canon 100mm macro]

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.

Puddling butterflies turned out to be remarkably skittish – in order to get a wide angle shot of these insects I had to leave the camera in the sand, and use a radio controlled trigger (seen on the left) to get the shots. [Canon 5D, Canon 100-400mm]

Puddling butterflies turned out to be remarkably skittish – in order to get a wide angle shot of these insects I had to leave the camera in the sand, and use a radio controlled trigger (seen on the left) to get the shots. [Canon 5D, Canon 100-400mm]

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.

This large aggregation of butterflies puddling in Guyana is probably made up mostly of male individuals. [Canon 1Ds MkII, Canon 16-35mm]

This large aggregation of butterflies puddling in Guyana is probably made up mostly of male individuals. [Canon 1Ds MkII, Canon 16-35mm]

To some butterflies, residues of my sweat were more tempting than the stuff in the sand (tapir – 0, me – 1) [Canon 5D, Canon 100-400mm]

To some butterflies, residues of my sweat were more tempting than the stuff in the sand (tapir – 0, me – 1) [Canon 5D, Canon 100-400mm]

The best spots to see large aggregations of tropical butterflies are often places visited by large grazers. Their dung often attracts many different species of insects seeking sodium and amino acids. [Canon 7D, Canon 16-35mm]

The best spots to see large aggregations of tropical butterflies are often places visited by large grazers. Their dung often attracts many different species of insects seeking sodium and amino acids. [Canon 7D, Canon 16-35mm]

Life in the season of death

Winter in the Northern Hemisphere – is there anything more unpleasant? To most entomologists living in temperate climates winter is synonymous with the disappearance of everything they love: insect activity and the pleasant buzz of millions of wings, vibrant colors of plants, warm weather. Our beloved animals have long turned to dust, buried themselves into the ground, or entered a stupor so deep that they might as well be dead. It will be long months before the word “green” re-enters our vocabulary, and both our skin and the ground below our feet breathe a sigh of relief.

A female snow scorpionfly (Boreus brumalis) is completely wingless and carries a long ovipositor. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

A female snow scorpionfly (Boreus brumalis) is completely wingless and carries a long ovipositor. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

But as I walked from my car to work this morning, trying with all my might not to expose any unnecessary fragment of my body to the frigid, dry air, I suddenly remembered that there was an insect, a very interesting one, that flourished in this dead season. I first saw it a few years ago in the middle of February on Wachusett Mountain in MA, jumping on the surface of deep snow like a black, shiny flea. It was a snow scorpionfly, a fascinating insect that up that point was only familiar to me from entomology textbooks.

Snow scorpionflies (Boreidae) are fascinating insects that can often be found on snow in temperate forests of the Northern Hemisphere. Their relationships are still somewhat mysterious —traditionally they have been considered a family of scorpionflies (Mecoptera), a group of agile, predaceous insects, but recent molecular and morphological studies suggest that they may be in fact more closely related to parasitic fleas. Regardless of their genetic affinities, these peaceful, moss-feeding creatures resemble little either true scorpionflies or fleas, and both their larvae and adults feed on mosses.

The male has highly modified wings that resemble a pair of scissors. He uses them to claps the female's elongated mouthparts during mating. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

The male has highly modified wings that resemble a pair of scissors. He uses them to claps the female’s elongated mouthparts during mating. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

But why are they active in the middle of winter? Bodies of all living cells contain a very high proportion of water, which turns into ice crystals when the temperature falls below 0°C, damaging the cell structure and potentially killing the organism. And yet, even in the middle of winter snow scorpionflies are not alone. Many arthropods have evolved physiological adaptations that allow them to survive and be active in subfreezing temperatures. As ectotherms, animals that cannot generate their own body heat, winter insects and spiders must possess the ability to supercool their body fluids in order to remain active in subfreezing conditions. Supercooling, a process that allows them to lower their body temperature to well below the water’s freezing point and still maintain its liquid state, is achieved by the presence of polyhydric alcohols and antifreeze proteins in their hemolymph and cells.

If he cannot get hold of her mouthparts, the male will sometimes grab the female's antennae to secure her position on his back. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

If he cannot get hold of her mouthparts, the males will sometimes grab the female’s antennae to secure her position on his back. [Canon 1D MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

Like other winter-active insects, snow scorpionflies take advantage of the fact that most predators that target insects disappear in the cold months, and come out in large numbers to mate. The larger and chunkier female is completely wingless, whereas the male has a pair of strangely modified, scissor-like wings, which he uses to clasp the female’s mouthparts and secure her position on his back during mating. After mating the female uses her long, external ovipositor to lay eggs in clumps of moss, where they will stay dormant until spring.

I have not seen scorpionflies this year, yet, but I will look for them. These animals may be about the size of a pinhead, but for me, in this season, they loom large.

Stalk-eyed flies

Stalk-eyed fly (Diasemopsis  fasciata) from Gorongosa National Park in Mozambique [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]

Stalk-eyed fly (Diasemopsis fasciata) from Gorongosa National Park in Mozambique [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]

I really don’t like when organisms that deviate from our narrow, anthropocentric perception of the natural world are described as “bizarre” but, let’s face it, flies of the family Diopsidae sure look that way. They are hypercephalic, which means that their head is extremely expanded in a way that places both their eyes and the antennae at the tips of very long, often almost horizontal stalks. This family of flies is not the only one that has eyes placed on long stalks, but in Diopsidae this feature is nearly universal. Diopsidae occur mostly in Africa and SE Asia, although two species are found also in North America and one in Europe. (One species is apparently quite common in Massachusetts, and I will definitely try to find it next summer.)

With eyes on such long stalks, keeping them clean is not an easy task. Not surprisingly, these flies spend a lot of time on personal hygiene. [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]

With eyes on such long stalks, keeping them clean is not an easy task. Not surprisingly, diopsid flies spend a lot of time on personal hygiene. [Canon 7D, Canon MP-E 65mm, 3 speedlights Canon 580EXII]

Although flies with hypercephalic features are considered a classic case of sexual selection driving the development of exaggerated morphological characters, Diopsidae don’t quite fit this explanation as both males and females have similar, greatly modified heads. In some species, however, sexual dimorphism exists, and males have longer eye-stalks than females. In such species females preferentially mate with males having the longest stalks, and these matings result in increased fitness of the females. Males engage in long, ritualized contests, where they clash with their heads, and the winner is almost always the individual with more widely separated eyes. This is because of a phenomenon known as hyperallometry – the larger the armament, the larger the body size, and thus the strength of the individual. Such contests serve as a simple way to assess the overall size of the rival, and smaller individuals will quickly give up the duel, sensing the strength of the larger rival.

It is not surprising that carrying your eyeballs at the ends of a long broomstick does not make your life any easier, and it has been shown that males who have particularly long stalks must also develop larger wings to compensate for the drag caused by their eyes. This, in turn, supports the idea of the “Handicap model” of sexual selection in these flies – because the long eye stalks make the male’s life more difficult, surely he must be a carrier of some excellent genetic material to be able to overcome the handicap of the gargantuan ornaments.

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Update (22 Jan. 13): Thanks to Hans Feijen for identifying the fly species, which turned out to be Diasemopsis fasciata, and not Diopsis.

Stalk-eyed flies usually spend the night in large roosts close to small bodies of water (Guinea) [Nikon D1x, Sigma 180mm, flash Nikon SB-28DX]

Stalk-eyed flies usually spend the night in large roosts close to small bodies of water (Guinea) [Nikon D1x, Sigma 180mm, flash Nikon SB-28DX]