Butterfly Caterpillar with Snake’s Tongue

Caterpillar of the Swallow Tail Butterfly defends itself by pushing out a ‘Y’ shaped organ that resembles a snake’s tongue. Called Osmeterium, the organ is a fleshy glandular sac, orange colored and when extended measures about quarter of an inch. The organ is unique to Swallow Tails.

Caterpillars of Spice Bush Swallow Tails are found on spice bush leaves. The caterpillar makes a tube, by cutting a portion of a leaf, folding it and spinning silk around the fold. It retreats into the tube for rest and when it is not feeding.

The caterpillar is velvety smooth and bright green. It grows to a length of a little over two inches and lasts up to thirty days, before entering pupal stage.

The caterpillar’s head is small followed by a swollen thorax. There are large black spots on its body that resemble the eyes of a snake.

On the first thoracic segment is the fork shaped Osmeterium. It lies hidden underneath a slit like opening. The caterpillar everts the organ by opening the slit. Body fluid pressure stretches the fork out. It is withdrawn within the lips of the slit, which close and hide the organ completely. The Osmeterium secretes foul smelling substances and releases them into air, when in action.

The tongue like organ, scent, color spots and caterpillar’s posture are combined to produce a defense to startle predators and scare them away.




When a bird approaches the caterpillar, the innocent looking creature suddenly everts the bright orange colored organ, like a snake thrusting out its tongue. The caterpillar assumes a snake’s attacking posture. The eye like color spots and foul smell give additional accent to the sudden transformation of the caterpillar. The predator is presented with an appearance that is shocking, surprising, unpleasant and scary, all in a single compliment.

No bird can dare try its bill on and have a taste of the shiny delicate skin of the Swallow Tail Caterpillar.