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Bypassing the cracks

An amazing evolution-defying design in a tiny insect

by Richard Peachey

AUGUST, 1929: in the sun-baked southeast African territory of Nyasaland (now called Malawi) medical entomologist (insect specialist) W.A. Lamborn discovered an extraordinary behaviour of the larva of the horsefly, genus Tabanus.

Photo by Darkone, Wikipedia.org

picture of The horsefly Tabanus

The horsefly Tabanus

Remarkable and novel

He wrote a detailed description, and sent specimens, to his long-time friend E.B. Poulton, an Oxford University professor and fellow of the British Royal Society. Poulton judged ‘this elaborate adaptation’ in the larva of a fly to be ‘so remarkable and novel’ as to warrant immediate communication to the Royal Society, which published Lamborn’s findings in one of its scientific journals in early 1930.1

Years later, George McGavin, a well-known Oxford entomology professor, came across the story. He described the unusual behaviour of Tabanus as an ‘ingenious trick’ which, he said, ‘is literally unique to this one genus of horsefly’.2

Amazing ‘one-off’ designs in nature

Recently, McGavin was asked by an Oxford colleague, the noted atheist and evolutionary zoologist Richard Dawkins, to come up with instances of ‘“good ideas” that have evolved only once’.3 Dawkins was looking for further examples to supplement two he already had in mind: ‘ … the wheel, with a true, freely rotating bearing, seems to have evolved only once, in bacteria, before being finally invented in human technology. Language, too, has apparently evolved only in us … .’4

In response, says Dawkins, Prof. McGavin referred to bombardier beetles of the genus Brachinus, which mix chemicals to make an explosion; and to the archer fish, which shoots a missile to knock prey down from a distance. He also gave an ‘honourable mention’ to antlions, spitting spiders, the bolas spider and the diving bell spider.5 But his ‘champion example’ of an evolutionary ‘one-off’ was the Tabanus horsefly.2 Dawkins assigned this fly a starring role in the climactic section of his latest book, The Ancestor’s Tale: A Pilgrimage to the Dawn of Life.

How the ‘ingenious trick’ works

Specimens sent by W.A. Lamborn from Nyasaland (modern Malawi)
to England in 1929 (from ref. 1).

HorseFlyFigsOneThree

Figure 1: Top of mud cylinder produced by a Tabanus horsefly larva, showing concave surface with hole resulting from emergence of the adult fly.
Figure 2: Shell of the pupa. (The larva is somewhat larger.)
Figure 3: Adult horsefly.

Click  for larger view.

HorseFlyFigsFourFive

Figure 4: Side view of mud cylinder. The larva entered the chamber at the level of collar ‘C’, just below the top of the cylinder. The close spiral tunnel made as the larva burrowed down is evident from the nearly horizontal grooves, especially visible on the right edge. Groove ‘G’ was made by the larva during its steep ascent to the surface, as it cut across the close spiral of its descent.
Figure 5: The same cylinder showing entrance ‘E’, which was sealed by the larva after penetrating the cylinder to construct its pupal chamber.

Click  for larger view.

When the Tabanus larva is ready to undergo metamorphosis (transforming itself into a pupa and then an adult fly), it buries itself in wet mud. But as the mud dries in the hot African sun it often cracks. So the pupating insect might suffer disturbance, overheating, and possibly predation—unless, as Dawkins explains, ‘ … it could somehow engineer a way for any crack that approaches it to be diverted around it instead. And it does indeed achieve this in a truly wonderful and probably unique manner.’2

While the mud is still moist, the larva fashions for itself a cylindrical protective chamber. Following a helical (coil-shaped) path, the larva tunnels down through the mud—in Lamborn’s words, ‘ … moving spirally, round and round in an almost perfect circle, so that the mud intervening between the spiral turns is so reduced as to form a very thin partition wall.’6

After reaching the correct depth of about 9 cm (3.5 inches), the larva next ‘corkscrews its way back to the surface in an opposite spiral.’2 This time it travels more directly, cutting sharply across the first spiral. ‘Then, at about half-an-inch [1.3 cm] below the surface the larva burrows into the cylindrical mass it has formed, seals up the entrance and hollows out the interior to form the pupation chamber … the pupa [is thus rendered] absolutely safe from sudden exposure when general cracking of the surface of the mud takes place.’7

‘Now, you see what this means?’ cries Dawkins, delighted. ‘The larva is encased in a cylinder of mud whose circular boundary has been weakened in advance by the preliminary spiral burrowing. This means that when a crack snakes across the drying mud, if it hits the edge of the cylindrical column, instead of cutting straight across the middle it goes instead in a curved bypass around the edge of the cylinder, and the larva is spared. It is just like the perforations around a stamp that stop you tearing the stamp across.’8

Missing the true significance

On the final page of his new book, Dawkins recaps by recalling several of the fascinating creatures he has already described, including ‘ … the horsefly larva with the apparent foresight to pre-empt cracks in the mud.’ He exults, ‘If it’s amazement you want, the real world has it all. … life on this planet [is] amazing, and deeply satisfying, to all whose senses have not become dulled by familiarity … ’. Agreed, so far. But then Dawkins concludes, ‘ … the very fact that we have evolved the brain power to understand our evolutionary genesis redoubles the amazement and compounds the satisfaction.’9

‘But ideal design is a lousy argument for evolution, for it mimics the postulated action of an omnipotent creator’—evolutionist Stephen Jay Gould

Amazing animal abilities, however, do nothing at all to improve the case for evolution! This was clearly understood by famous evolutionist Stephen Jay Gould. He said: ‘Our textbooks like to illustrate evolution with examples of optimal design … . But ideal design is a lousy argument for evolution, for it mimics the postulated action of an omnipotent creator.’10

Gould recommended instead a so-called ‘dysteleological’ argument: ‘Odd arrangements and funny solutions are the proof of evolution—paths that a sensible God would never tread but that a natural process, constrained by history, follows perforce.’11

But such an argument is plainly theological (based on the presumed nature of God) rather than scientific (based on what can actually be observed).12

Furthermore, dysteleological arguments have proved to be notoriously problematic. As evolutionary philosopher of science Daniel Dennett points out, ‘There is simply no denying the breathtaking brilliance of the designs to be found in nature. Time and again, biologists baffled by some apparently futile or maladroit bit of bad design in nature have eventually come to see that they have underestimated the ingenuity, the sheer brilliance, the depth of insight to be discovered in one of Mother Nature’s creations. Francis Crick has mischievously baptized this trend in the name of his colleague Leslie Orgel, speaking of what he calls “Orgel’s Second Rule: Evolution is cleverer than you are.”’13 [Emphasis added]

How sad that such highly educated and intelligent people fail to give credit where it’s due! Even when face to face with the Creator’s awe-inspiring wisdom as seen in the created order, they will not acknowledge Him, praising in His place a personified ‘Mother Nature’ or ‘Evolution’.

‘For although they knew God [that is, they understood his power and divine nature from what they clearly saw in creation], they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened’ (Romans 1:20–21). ‘For the wisdom of this world is foolishness in God’s sight’ (1 Corinthians 3:19a).

In our present fallen world, we don’t usually consider horseflies as evidence of a benevolent supernatural Designer. Instead, we view them as nasty bloodsucking disease-infested pests!

Male horseflies are nectar feeders, but females drink the blood of horses and other large mammals to obtain nutrients for egg production. As they move from one animal to another they often carry pathogens (disease-causing microbes). Medical entomologist W.A. Lamborn (see main article) was studying African horseflies because he suspected they might transmit trypanosome infections (he was right).

In God’s original ‘very good’ creation, before Adam and Eve’s sin, the creatures we now call horseflies likely dined on green plants (Genesis 1:29–31). Even now, some African species feed on the sap of plants.

Today, horseflies serve as reminders that we live on a ‘cursed’ earth (Genesis 3:17) which ‘groans’ in pain (Romans 8:19–22). But thanks to the work of Jesus Christ on the Cross, believers can look forward to the time when pests, pathogens and parasites will all be in the past, and ‘there will be no more death or mourning or crying or pain’ (Revelation 21:4)—the Genesis Curse will have been removed (Revelation 22:3).

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