Wednesday, 15 October 2008

The Elaterid Clicking Mechanism

..... or How Click Beetles Click

We all know Click beetles (family: Elateridae) click and jump but how do they do it? These beetles will jump to confuse a predator and the technique is also pretty handy for righting themselves if they end up on their back. I have tried to photograph the clicking mechanism in the past without success but a deceased Click beetle made the job a little easier.

How it works

The first segment of the thorax (prothorax) is loosely hinged to the middle segment (mesothorax). Now lets looks at the underside of these two segments. The plate on the underside of the prothorax is known as the prosternum. It has a backward pointing, spine-like process (prosternal process). It slots neatly into a corresponding cavity on the mesosternum (mesosternal cavty)

OK so you've got all that, theres a pointy bit and a corresponding groove or cavity :-) Now think about what happens click your fingers. You put your finger and thumb together and apply pressure until your finger suddenly slips away from your thumb with quite some force. Likewise, the beetle inserts this process (pointy bit) into the cavity and then arches back putting pressure on the process until it suddenly releases from the cavity, springing the beetle into the air.

So just how good are they at righting themselves? One study ran several thousand tests on four species of Elaterids which showed a success ratio of 2 to 1 if the beetle was initially lying flat on it's back. The success was shown not to be through the beetles selecting a particular path through the air but by the body shape having a disposition toward attaining an upright position. Randomly dropping dead or live click beetles on the floor gave a similar success rate in landing in an upright position. On an inclined surface the success rate was as high as 85% to 90%. Thus it seems that the increased chance of rolling or bouncing also increases the success rate in landing upright.


(Click Photos to Enlarge)
#1 - The clicking mechanism of an Elaterid beetle


#2 - Ventral view of an Elaterid beetle highlighting the region shown in image #1



References:
  • Program and Abstracts of Scientific Papers Presented at the Marine Biological Laboratory, Summer of 1944 - Biol Bull 1944 87: 153-166


3 comments:

  1. Finger-clicking good!
    Some may remember toy tin frogs with spring steel powering similar random leaps.

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  2. Thanks Tony - Yeah I remember those frogs :-)

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  3. Fascinating stuff Mosura, the earwig too. You've added to my knowledge considerably.

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