Praying mantises, crickets, and honeybees respond to injections of the pain-killing opioid drug morphine with lower defensive responses to an unpleasant event, and the strength of the response is proportional to the morphine dose. This analgesic effect can be blocked by a drug, naloxone, that counteracts morphine’s effects in vertebrates. These studies suggest that insects have a general sensitivity to opioids similar to that of vertebrates.
