Solved my riddle - it is not a mealybug! It is a Mealybug Destroyer (Cryptolaemus montrouzieri )- a beneficial insect that preys on mealybugs and aphids. That's why they're concentrated by the aphids. Sure looks a lot like a mealy at first glance though!

BP

Look closer to see if the aphids are disappearing into one end of the larvae. Probably some kind of beneficial that is where the aphids are because it is eating them. Otherwise, it should be possible to see them eating the asparagus.

It is eating the aphids. It's part of why I thought they possibly weren't mealys. They are definitely beneficials - Mealybug Destroyers (their preffered prey is supposed to be mealys, but they'll eat aphids too). I'm not sure where it came from though. They aren't supposed to be able to withstand my winters, and prefer warm coastal climates. I'm in the middle of a large, inland, northern city, far from agricultural areas. I've never seen one before.

BP

The adults are brown and black ladybugs. Perhaps you've see some of them flitting around, too. There had to be at least one to lay the eggs that hatched into this neat larvae.

Perhaps the insect came in on some plants that you purchased. Or even as an accidental migration.

A few days ago, DH was asking me about a bug he saw with a reddish head - I figured it was a soldier beetle. When I showed him a pic of the adult mealybug destroyer, he said that was it. I haven't seen any so far, but I'm keeping my eye out now.

It's possible it blew in from someone around here that purchsed them for pest control. I haven't bought any new plants in the past month, but some neighbour could have bought one with this hitchiker on it. According to what I read though, they lay their eggs in the cottony nests of mealybugs. Either I have no mealybugs, or I have so few that I can't find them, but I hunted all over this morning looking for a mealybug nest, and there weren't any to be found (unless the destroyers already ate them...).

I'm happy to have a neat new beneficial in my garden though - even if it is only for a short time :-)

BP

With beneficials, you're good for more.

If the adults are capable of flight then they can get around pretty well on their own.