Sentinel Tick

This particular insect is known to have a particular type of neurological system, making it particularly easy to train. They can be made to associate a particular chemical signature with nutrition, and this association persists for up to 30 generations.

A tick hive can then be installed at line stations or other secure installations, where they provide only a minor irritation to most users, but swarm in the presense of certain chemicals (usually explosives, or the odour of foodstuffs for which there are import/export restrictions). This kind of alarm is significantly cheaper than an electronic gas sampler, and can also more easily identify which bag contains suspect materials. In some circumstances, sufficient numbers of insects can even incapacitate a terrorist.