Burrows and Sutton needed more evidence. Analysing the movies, the duo could see that the insects continued accelerating during take-off, even when the trochanter (knee) was no longer pushing down. And the insects that jumped without using the trochanter (knee) accelerated in exactly the same way as the insects that jumped using the trochanter (knee) and tarsus (toe). Also, when Burrows and Sutton looked at the flea's leg with scanning electron microscopy, the tibia (shin) and tarsus (toe) were equipped with gripping claws, but the trochanter (knee) was completely smooth, so it couldn't get a good grip to push off. Sutton and Burrows suspected that the insects push down through the tibia (shin) onto the tarsus (toe), as Bennet-Clark had suggested, but the team needed one more line of evidence to clinch the argument: a mathematical model that could reproduce the flea's trajectory.
'I looked at the simplest way to represent both models,' explains Sutton. Building Rothschild's model as a simple mass attached to a spring pushing down through the trochanter (knee) and Bennet-Clark's model as a spring transmitting the spring's force through a system of levers pushing on the tarsus (toe), Sutton generated the equations that could be used to calculate the insect's trajectory. Then he compared the results from his calculations with the movies to see how well they agreed.
Both models correctly predicted the insect's take-off velocity at 1.35m/s, but then the Rothschild model began to go wrong. It predicted that the insect's acceleration peaked at a colossal 22,000m/s2 (2200g), whereas the acceleration of the insects in the movies only peaked at 1500m/s2 (150g). However, Sutton's calculatio
|Contact: Kathryn Knight|
The Company of Biologists