On the hunt for explosives Baranidharan Raman/Washington University in St. Louis

Move over, sniffer dogs: now there are explosive-sensing grasshoppers. Barani Raman and his colleagues at Washington University in Missouri have tapped into the olfactory senses of the American grasshopper, Schistocerca americana, to create biological bomb sniffers.

In insects, olfactory receptor neurons in their antennae detect chemical odours in the air. In turn, these neurons send electrical signals to a part of the insect brain known as the antennal lobe. Each grasshopper antenna has approximately 50,000 of these neurons.

To test bomb-sniffing ability, the team puffed vapours of different explosive materials onto grasshopper antennae, including vapours of trinitrotoluene (TNT) and its precursor 2,4-dinitrotoluene (DNT). As controls, they used non-explosives such as hot air and benzaldehyde, the primary component in the oil of bitter almonds.


By implanting electrodes into the antennal lobes of grasshoppers, the researchers found that different groups of neurons were activated upon exposure to the explosives. They analysed the electrical signals and were able to tell the explosive vapours apart from non-explosives, as well as from each other.

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The team fitted grasshoppers with tiny, lightweight sensor backpacks that were able to record and wirelessly transmit the electrical activity of their antennal lobes almost instantaneously to a computer.

The grasshoppers continued to successfully detect explosives up to seven hours after the researchers implanted the electrodes, before they became fatigued and ultimately died.

The process immobilised the grasshoppers, so the researchers put them on a wheeled, remote-controlled platform to test their ability to sense explosives at different locations. The grasshoppers were able to detect where the highest concentration of explosives was when the team moved the platform to different locations.

The team also tested the effect of combining sensory information from multiple grasshoppers, given that in the real world chemicals might be dispersed by environmental factors, including wind.

Taking neural activity from seven grasshoppers yielded an average accuracy of detection of 80 per cent, compared with 60 per cent for a single grasshopper.

The project was funded by the US Office of Naval Research and the researchers believe the grasshoppers could be used for homeland security purposes.

A limitation of the study was that it didn’t test the grasshoppers’ explosives-detecting ability when multiple odours were present at the same time.

Reference: https://www.biorxiv.org/content/10.1101/2020.02.10.940866v1