Crawlies with Cri: Common blue mud-dauber (Chalybion californicum)

Common blue mud-dauber (Chalybion californicum)

This week’s crawly is positively waptastic and she wants you to know, “Don’t panic” if you see her. Meet the common blue mud-dauber (Chalybion californicum).
At three-quarters of an inch to one inch in size, common blues are good-sized wasps and their wicked cool metallic blue coloring makes them eye-catching as well.
You’re likely to spot common blues in one of three places: 1. Around the eaves or siding of your house where mud-daubers may build nests and like to search for spiders; 2. Gathering water from a pond, creek or puddle (we’ll get to why in a bit); or 3. Drinking nectar from pretty posies.
Let’s back up to “like to search for spiders”. Mud-dauber wasps (Tribe Sceliphrini) are solitary wasps who provision their nests with spiders for their young. Remember, solitary wasp females each build their own nest versus living in a hive with lots of other wasps.
In the case of the common blue “build” is a bit of an overstatement. These clever girls don’t go to all the work of constructing a complex nest from tiny balls of mud like their cousin mud-daubers do. Instead, they remodel old, abandoned nests of black and yellow mud-daubers.
It’s like “This Old House” for wasps. The common blue will gather water, use it to soften the dried mud of the unused mud-dauber nest and reshape it to her liking.
So, you’ll only see common blue mud-daubers if you also have the flashy black and yellow species around as well.
Once Ms. Blue has her fixer-upper fixed up, she’ll go on a spider hunt. The preferred prey of common blues are black widow spiders. Yep. You read that right. These metallic beauties are among the black widows’ few predators.
To be clear, don’t assume you have black widows if you see a common blue searching around your house. They will take any number of species in the family widows belong to (cobweb weavers – Family Theridiidae). In a pinch, they’ll also take lynx and crab spiders.
Common blues have the cool ability to avoid getting stuck in spider webs. They’ll walk onto a web, then put on a show of being “helpless prey” and when the spider comes out to catch them the blue will instead sting the spider and carry it away.
The common blue’s refurbished nest is made up of several individual mud cells. She’ll put one spider at the bottom of a cell, lay an egg on it, then tuck in more spiders as food for the young. Each cell is individually sealed off with a mud cap.
Young will hatch, then chow down on several spiders until they are mature/large enough to spin themselves into a silken cocoon and morph into adult form. If it’s early enough in summer, they’ll emerge right away to search for their own abandoned nest to fix and spiders to catch.
Those who reach adulthood late in the season will overwinter in their mud cell and emerge the following spring. In our area, most adults are seen in late July and early August. If you didn’t get a chance to see one this year, keep an eye out next summer because these beauties are worth seeing.