Archive | October 1, 2012

Be glad that we are big

An antlion larva from Costa Rica – its large body serves as an anchor, permanently buried in the sand, while the head on a long “neck” is the weapon that catches the prey. [Canon 7D, Canon MP-E 65mm, 3 speedlights 580EXII]

If there existed a technology that would allow us to shrink all people on Earth to the size of insects (just like in the movie “Honey, I Shrunk the Kids”), two things would almost certainly happen over the next few years. First, nearly all our environmental problems would be solved because the use of natural resources is correlated with body size not in a linear, but a logarithmic fashion. This means that the pollution that we produce, resources that we use, and the land area that we need to live would decrease by many orders of magnitude. Second, a huge proportion of our population would quickly fall prey to things that we often do not realize exist, and a lot of the carnage would happen in places inhabited by antlions.

Imagine walking on a beach, minding your own business, and enjoying the sunshine. Suddenly, the ground below your feet shifts, and you are sliding down a deep pit in the sand. “Bummer”, you think, as you dust yourself off and begin to climb out. But before you can reach the rim of the hole, a barrage of rocks starts hitting your head, and you lose your balance and tumble back to the bottom. And there, a pair of giant clasps snatches your body and immediately pulls you under the sand, and seconds later a powerful venom is injected into your veins. You are dead.

An ant desperately tries to leave the sand pit, but a sudden explosion of sand sends it back to the bottom, straight into the jaws of an antlion. [Canon 7D, Canon 100mm, 2 speedlights 580EXII]

Believe it or not, but this scenario is part of a daily routine for many small organisms, ants in particular. Not having a very good vision, ants cannot see the sand pits created by antlions, which are sit-and-wait predators, larvae of the members of the family Myrmeleontidae (Neuroptera.) Antlions are particularly common in areas that are covered with fine sand and not particularly windy (too much wind would force them to rebuild their pit traps too often.) Thus, they can often be seen in partially sheltered locations, such as under overhanging rocks or on sandy roads within forests. Their pits have walls that use the critical angle of repose – they are as slanting as physically possible, and will start collapsing at the slightest disturbance, such as when an ant tries to climb up them. If this wasn’t enough, the antlion larva makes sure that nobody can get out of the pit by hurling sand and pebbles at the insect trying to make an escape.

As larvae antlions are not particularly handsome creatures – a fat, hairy body with spindly legs carries a large, flat head with massive jaws, situated at the end of a long, curved neck. Interestingly, you will not find the element that seems critical for any successful predator on the head of the antlion larva – a mouth. Rather than chewing and eating their prey in a traditional fashion, antlions employ a strategy more typical of spiders than insects. Their long mandibles are essentially syringes that first deliver digestive enzymes into the body of the victim, then, once this extra-intestinal digestion is completed, the liquified content of the victim’s body is sucked through the same organ.

An adult antlion (Palpares sp.) from South Africa [Canon 1Ds MkII, Canon 180mm macro]

Even more surprising is the lack in the antlion larva of another, seemingly indispensable body part, which everybody, predator or not, should probably have. I am talking, of course, about the anus. But no matter how hard you poke and prod the poor creature, you will not find one as the midgut ends without an opening inside the abdomen. Turns out that antlions go through their entire development without going No.2 even once (they do, however, go No. 1, by excreting allantoin, a product of uric acid metabolism.) Only after they emerge from a pupa many months later, as gossamery, damselfly-like adults, do they relieve themselves of the accumulated waste (known as meconium) through a newly acquired opening at the end of the abdomen. Adult antlions feed mostly on pollen, although some of them retain their taste for insects, and hunt flies and other small things in flight.

A larva of an owlfy waiting for a victim on a tree in Botswana [Canon 10D, Canon MP-E 65mm, Canon MT-24EX twin light]

Close relatives of antlions are owlflies (Ascalaphidae), which follow a similarly insidious lifestyle as larvae, snatching unsuspecting passersby with their long, sharp mandibles. Unlike antlion larvae, they do not build pit traps in the sand, but rather wait, perfectly camouflaged, on tree trunks or leaves. Sometimes they adorn their bodies with grains of sand to enhance the illusion of being just a part of the background. Adult owlflies are also predaceous, and catch their victims in flight, the way dragonflies do. They are strong fliers, much better than adult antlions, but can be easily distinguished from both antlions and dragonflies by the presence of long, clubbed antennae.

The lesson here is that life of insect-sized creatures is no picnic, and our gargantuan size has some gargantuan advantages. There really are no dangers equivalent to antlions at our spatial scale (real lions don’t set up pitfall traps and throw rocks at their prey.) But, just in case somebody invents a body-shrinking machine and unleashes its powers on the unsuspecting world, it is good to know what to expect.

An adult owlfly from Mozambique [Canon 7D, Canon 100mm, 2 speedlights 580EXII]