I’ve been watching and photographing a couple of huge Orchard Swallowtail Caterpillars for the past week and they are the biggest caterpillars I have seen.  I was keen to keep an eye on them to perhaps be lucky enough to witness the transformation to cocoon and butterfly. If you get upset easily you may not want to read this story.

Orchard Swallowtail Caterpillar in defense mode

It takes four weeks for the caterpillar to mature, ready to turn into a pupa and these ones in my garden are very developed.  They have a “Y” shaped gland behind the head, the osmeterium which you can see in both of the above photographs I took.  This pops up when the caterpillar senses danger and it is a bright red colour which I also noticed gives off an odour so I wasn’t game to get too close!

After Christmas, I photographed them again but there was another critter on the branch sitting very close to one of the caterpillars which I didn’t think anything of until I went out again the next day and the caterpillars were gone – they had completely vanished! I searched for a pupa or anything that remotely resembled one but found nothing.  I was intrigued then about the other bug and when I found out what it was I was completely horrified!

Here is the evil “bad guy” and he was actually killing the caterpillar!  He is an assassin bug, named because of the way they feed on their prey. If you look closely you will see that he is piercing the caterpillar with a sucking mouthpart which is a weapon (proboscis) with which to kill other insects.  He is sucking out the body fluids of the caterpillar and feeding on them – you can see why I was horrified and it explains why the caterpillars had vanished.  I was upset for the rest of the day after discovering this.

The orchard swallowtail butterfly – what might have been …

Orchard Swallowtail Butterfly