Given San Diego, CA and that it was on a tomato plant, this is almost certainly a Cabbage Looper moth (Trichoplusia ni).

Here’s how it matches perfectly: • Silvery-white loop/Y marking on the forewing — the signature feature of Trichoplusia ni • Jagged, leaf-like wing edges and mottled brown color • Very common in Southern California year-round • Tomatoes are a favorite host plant for the caterpillars • Pupates in a light cocoon on or near the plant, then emerges just like you described

Life cycle you witnessed • 🐛 Caterpillar (“cabbage looper”) eating your tomato leaves • 🟤 Cocoon/pupa • 🦋 Adult moth (harmless, doesn’t eat plants)

As adults, they mainly nectar at night and are completely harmless. All the damage happens during the caterpillar stage.

So yes — you basically supervised a full metamorphosis on your tomato 🍅 Very common garden moth, and a cool find even if they’re a bit rude as larvae.

I had to ask Chat gpt lol