Two reservoirs hold hydroquinones and hydrogen peroxide separately. When threatened, the beetle admits them to a thick-walled reaction chamber containing catalases and peroxidases, which decompose the peroxide and oxidise the hydroquinones. The reaction is strongly exothermic, bringing the mixture to roughly the boiling point of water and generating the gas pressure that expels it.
Synchrotron X-ray imaging published in 2015 resolved the discharge in living beetles and found it pulsed at rates on the order of hundreds of times per second. Each pulse follows a cycle in which pressure closes the inlet valve, the charge is ejected, and pressure drops enough for the valve to reopen. Pulsing appears to protect the beetle from the heat it generates while sustaining the jet.
The beetle can aim. A revolving abdominal tip and deflecting structures direct the spray towards an attacker, including forwards over the beetle's own back, and toads that have swallowed one have been recorded vomiting it up alive.