

What you can't tell from the photos is that he's just over 1 cm long. In my opinion, he is a fresh third-grader, having spent the winter in 2nd instar. Most years, a number of cats do this (the normal, 'book' behaviour is to hibernate in 3rd instar) but I didn't expect it this year as last year the eggs were laid so early. Why should a caterpillar not go through to 3rd instar? Anyway, this little chap looks like a third-grader and Frohawk states that after the second moult (from 2nd to 3rd instar) the caterpillar is 13.5 mm long, including the horns. He is no longer than that, if that.
Frohawk also states that shortly before the fourth moult (into 5th instar), the caterpillar is 22.5 mm in length, including the horns. Faith is at least 22.5 mm long - I estimate a little longer than that - so she would seem to be laid up for moving into 5th grade. I'm still very confused about this, as she should be nowhere near this stage at the beginning of May. Her friend, Willow, is over an inch (25 mm) long. Here they are this evening:

(Faith)

(Willow)
If they escape the predators, I'll know the truth for certain as they continue to grow up.
White admiral cats are hard to find at the moment. Here is one:

I had to use flash for many of these pictures because of the fading light.
Guy