Gwynne, that cat is probably about 3 days old with how big it is. Here is a pic of a newly hatched caterpillar, not until the second day can you usually even see the stripes starting to form. I think an egg is easier to spot then a newly hatched cat.
I have looked through lots of patches and not found anything too. It is quite time consuming looking around all the leaves. The smaller cats usually can be found on the uppermost leaves, the bigger ones pretty much anywhere. The smaller plants usually will have the most egg/cat activity.