Beautiful caterpillar

I just had to share a photo of this beautiful caterpillar, which I found on Passiflora arbelaezii.  I collected a pair of them a few days ago and they are growing fast.  I think it is a Dryas julia larva but will confirm when it ecloses from the pupa in a couple of weeks.  Dryas is related to Heliconius.  These larvae release very little or no cyanide gas when feeding on this highly toxic plant.  My measurements indicate that the leaves contain 3-7 micromoles of HCN per gram of leaf tissue, making it one of the more toxic species of Passiflora.

I measure HCN gas using a meter (yellow device in rear of photo) designed for emergency responders entering buildings with hazardous materials.  To use the meter effectively I had to deprogram all the built-in alarms, including physically removing the vibration alarm.  The built-in alarms were programmed go off at 4.7 part per million (ppm) cyanide gas (low alarm indicating danger) and at 10 ppm indicating extreme danger (get out!).  A square centimeter of crushed P. arbelaezii leaf is enough to set off the high alarm right away, but this caterpillar, even when rapidly feeding, usually releases no measurable amount.   The apparatus includes a special pump (yellow device center photo) which moves 5 milliliters of gas each second.  The ppm reading, along with the known volume of the glass flask enclosing the sample enbles me to calculate the micromoles of HCN gas contained in the flask.  The flask in the photo contains a Heliconius hecale larva feeding on P. arbelaezii.  The larva consumed the toxic plant with no difficulty.