Spectrum with the x axis showing the frequency so that 0.5 is half of the measuring frequency (in this case 20Hz and so it measures until the Nyquist frequency: 10Hz).Here we see the result for the three platforms without any flies. From time to time I hit the table to make some signal in the platforms

To compare the power of the frequency put together platform with (green and black) and without flies (red). This is the case of three different flies in each platform.

Here the same flies, just in different platforms. There we see that some platforms show stronger signal than other (if I remember well). So is not the fly making the difference. But I have to check. Measuring in this case the 250Hz raw data. In black with a fly and in red without fly

Measuring in this case the 250Hz raw data. This time with and additional fly (green). We can see a characteristic peak at around 60Hz.