Caterpillars found to exhibit a stationary method of coping with distress, adopting the sphinx position.

In a groundbreaking study published in the journal Biology Letters, scientists at Tufts University have discovered that tobacco hornworm caterpillars (Manduca sexta) exhibit an extraordinary behaviour when injured or in discomfort. This behaviour, known as the sphinx state, is unlike the fight-or-flight response seen in most animals.

The study, authored by Michael Douglas and Angela Douglas, reveals that the sphinx state is an 'evoked' response, initiated on sensing an external stimulus. When caterpillars experience mechanical disturbance in their surroundings, they enter this motionless state, which is reversible. This behaviour is not a reflex but an actively chosen behaviour by the caterpillars, indicating a level of consciousness and control.

Interestingly, when caterpillars were separated from external mechanosensory stimuli for 24 hours, none of them entered the sphinx state. This suggests that the sphinx state is not a constant condition but is triggered by specific environmental cues.

The study also found that the cerebral ganglion, a brain structure that controls movement and processes sensory information, could not trigger the sphinx state on its own. This finding challenges the traditional understanding of nociception as strictly hard-wired and stereotyped.

The unusual behaviour of tobacco hornworm caterpillars could potentially help scientists rethink pest control strategies. By understanding the mechanisms behind the sphinx state, researchers may be able to develop smarter and safer ways to manage crop pests without relying solely on harmful pesticides.

Moreover, this study offers a window into the biology of pain. The findings could lead to novel ideas for developing new kinds of pain relief in humans. The sphinx state is a novel instance of active behavioural modulation in insects and highlights the flexibility of nociceptive responses.

The Tufts team plans to explore how widespread this behaviour is in the insect world and to trace the exact neural circuits responsible. Their research could reveal new insights about how animals process pain, potentially leading to a better understanding of pain mechanisms in humans and other animals.