A Beetle’s Screw And Nut

Science 2011 Jul 333(6038) 52, Fig. 1.png

The 3D reconstruction [(A) to (E)] of coxa (green) and trochanter (yellow) of left hind leg of T. oblongus. (A) Depressed position. (B) Elevated position. (C) Coxa cut horizontally along rotation axis; dorsal aspect of trochanter while leg depressed. (D). Isolated trochanter showing external spiral thread and tendon (t). (E) Dorsal portion of coxa corresponding to ventral portion of (C). (F) Scanning electron microscope photograph of the right metatrochanter showing posterior condyle (c) and external spiral thread (e).

This stunning image reveals for the first time that beetles use a screw and nut mechanism for leg movement. Scientists used very high resolution X-ray imaging to prove this and found that it is widespread amongst weevils. Do you see beauty in this?

While this does allow freedom of movement, one possible disadvantage is that “when fully tightened, the joint comes to a dead stop.”

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According to the authors:

We report the finding of a functional screw-and-nut system in the coxa-trochanteral joints of the legs of the Papuan weevil Trigonopterus oblongus (Pascoe) (2). We reveal the system’s structure and function through interactive three-dimensional (3D) reconstructions created from synchrotron-based x-ray microtomography (μCT) (3) of museum specimens.

The three major joints of an insect leg, the coxa-trochanteral, trochantero-femoral and femoro-tibial articulations, are usually considered as hinges (4). However, in the species of hyperdiverse Trigonopterus weevils studied here, the coxa-trochanteral joint is highly modified and allows rotational movement combined with a single-axis translation.

…apical portions of the coxae closely resemble engineered screw nuts.

It is remarkable that in the case of the weevil leg a rotary movement is accomplished by a screw-and-nut system. In engineering, such systems are mainly used for fixing connections, whereas an axle would be used for a simple rotation.

Comments

  1. #1 Emory K.
    July 12, 2011

    “In engineering, such systems are mainly used for fixing connections, whereas an axle would be used for a simple rotation.”

    Well, something kinda similar _is_ used in engineering for simple rotation – a worm gear.

    Unfortunately, it’s semantically and taxonomically confusing to refer to a worm gear in a beetle.

  2. #2 Art
    July 12, 2011

    Maybe we should rename the “worm gear” the “beetle gear.”

    How long will it be before the IDers claim this paper as evidence of design?

  3. #3 Lassi Hippeläinen
    July 13, 2011

    The IDs have already pwned the story. And speaking as an engineer, I’m happy to point out that the alleged Designer isn’t Intelligent. There are better uses for screws, and there are better ways to make a moving joint.

  4. #4 David Esau
    August 1, 2011

    Ingenuity never was solely about mechanics, but rather it should fold the best aspects of a number of disciplines into a single, model-of-efficiency design (and unfortunate as this may be, we often regard these disciplines separately).

    In this case, consider the fluid differential between limbs moving with readily discernible cadence; the entire organism is encased within a semi-rigid capsule, appointed with symmetrical pairings of hyper-elastic membranes in conjunction with each of the mechanical joints depicted. So we might observe compound hydraulic pressure differential, working in synchronous concert with each sequential limb extension/retraction.

    Sure, the challenge posed here is thrilling for us humans to get our brain around, just speaking as a non-engineer.

    Mechanically, these mated components are helical levers. In hydraulic terms, each represents a compact, *reciprocating* rotary torque converter. I would want to investigate further, whether the design regulates a resonant, acoustical standing wave within the encapsulated fluid, achieving a variable stiffening behind each helical joint, and optimizing output of muscle mass while effecting joint rotation/counter-rotation.

    It’s the automatic transmission all over again; PowerGlide performance, three opposed pairs, two limbs each, working their tails off to extend the optimum locomotive response across a finite range of demand.

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