As requested, I raised the caterpillar indoors. Here are photos of the resulting moth and empty pupal case. Caterpillar was about 7mm when it pupated, moth less than 25 mm wingspan. Original caterpillar photo was 17 March.
Can you take it into protective custody, rear it to get a moth, then take the moth back and release it where it came from (taking a photo of the moth first)?
Not many Geometrids recorded on Rutaceae before. Very interesting. Your tower caterpillar may have died, pupated, or emerged long ago. Was it not there before? Has it since moved from its original spot?
Don I am sorry, it may have been there previously. I only noticed it two days ago. I don't think it has moved, so case may be empty. Will keep checking. Re the looper, I had a brown one just like it on a pelargonium last year, sighting on Canberra Nature Map for unidentified Geometer moth. Thanks Jacky
The most obvious difference between E. excursaria and E. bispinaria is the shape of the black hindwing submarginal line where it meets the costa, which junction is obscured by the forewing in your photo.