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I descnbe the selection of hard particles for case building in caddis fly larvae. The larvae prefer large and flat particles which are more profitable in terms of time and silk thread spent for building. When larva discover particles of various profitability in a random sequence, one may expect the sequence of larva's choices to be also random. However, the larvae tend to repeat acceptances and rejections of particles . This repetitive response sequence results in a partial choice of unprofitable particles. I developed a model of selection based on simple rules that real larvae use. The model qualitatively reproduces the preference for more profitable particles, as well as the repetition of responses and the partial choice. In the model, a random sequence of discovered particles is viewed upon as an external noise. The non-linear control mechanism transforms the noise into the repetitive behavioural sequence. Thus, the behaviour of model is the result of self-organisation in noise-driven system. I discuss how the seif-organising order may interfere with adaptive behaviour.