Wednesday, September 12, 2012

Wasp Wednesday

Wasps, bless their hearts... no one ever has anything good to say about wasps. While it is true they can sting, many species just mind their own business when away from their nests and are not overly aggressive unless threatened. So here's a little information about a few of our most visible wasps in hopes of reducing the chance of a negative encounter.

N.B. CDC has a document on how to deal with insect bites as well as an identification key to stinging hymenoptera (wasps, bees, ants). CDC also offers this link on how to handle insect stings (how to administer first aid, knowing when to seek additional medical assistance, etc.).

Let's start with the pretty blue mud dauber. This is a solitary wasp who, among other things, catches and feeds black widow spiders to its babies. [In case you wonder, yes, we do have black widow spiders in the neighborhood so please wear gloves when working outdoors]. The blue mud dauber nests in underground cavities built by other wasps or by its spider victims.

Pretty in iridescent blue, but fear not, only ~1" long.

You have probably seen the nests of other mud dauber species--they like to build on the sides of buildings and other sheltered areas. Mud dauber wasps are recognizable by the narrow, string-like passage that connects thorax to abdomen. They are solitary: a female establishes a nest, lays eggs, shuts the egg in (with a full supply of food) and the kids raise themselves. Should you break a mud nest open, you would find it jam-packed with paralyzed prey for the wasp's larvae to feed on.

Black and yellow mud dauber nest. This expressive individual
 eschewed the traditional "mud" color and went for a patchwork effect.  The open cells
tell us that this generation of wasps already emerged. A closer look reveals
empty crypts and leftover legs... 
... just legs, lots of them. Spider legs, looks like. 

Here's a close-up, with better lighting, of the back side of the above nest.
Can't help but think it would be fun to match the colors to Benjamin Moore paint chips...
I checked with Dave Butler to see if he could shed some light on what materials The Artful Wasp used to create her nursery and he said that
"It's likely that she used soil with organic material making it different colors. The soil in our area is made up of weathered gneiss (metamorphic rock) containing quartz, feldspar, and mica. The feldspar and mica weather to produce our clay, made red by oxidizing iron."  

Next up, say hello to a common paper wasp (a.k.a. northern or golden paper wasp), Polistes fuscatus. According to Discover Magazine, this species has very good vision and is surprisingly good at recognizing familiar (wasp) faces. This is a social wasp, and you need to be careful because social wasps will defend their nest if threatened. In other words, a foraging wasp will mostly ignore you, but that same wasp may become defensive should she find you standing too close to her nest. And if she is alarmed enough, she may release a chemical message to her sisters and brothers to join the fight.

When you find a wasp nest (much like a bee colony), you are looking at a family group established by a female equipped with an ample supply of stored sperm. In the case of Polistes, mating happens in fall and the future queen overwinters, then starts a new colony in spring. The nest starts small and as the first eggs hatch, the queen feeds the hatchlings and grooms them. As those larvae grow into adults, they remain at home and help care for their younger siblings. And so grows the colony.

Polistes nest. Typically, the oldest siblings hatch from the earliest cells
towards the middle of the nest. Closed cells in the periphery have
larvae that have pupated and will emerge as adults. 

Same nest, photographed ~2 hours apart. The males have yellow faces and curly antenna tips.
The large larva to the left was quite active and moving around when the photo was taken but two hours later had built a privacy screen. It can now concentrate on reinventing itself into an adult wasp.  Click to enlarge.

Another common Medlockian is the red paper wasp, who is also in the genus Polistes and also builds paper nests. You will see this one fleeting around flowers while collecting nectar, but they are also known to feed on caterpillars.

Red paper wasp, with protein on its mind?

Spray me, maybe

Now for the scarier wasp types: yellow jackets (Vespula sp.) and bald-faced hornets (Dolichovespula maculata). As with the social wasps above, colonies start with a single individual that overwintered. By the end of summer, a queen may build a nest that houses hundreds of individuals. As colonies grow and food supplies diminish with the advancing season, these insects may be drawn to food scents in areas being used by people. Summer of course is a time when people spend more time outdoors, whether relaxing, exercising, or doing routine maintenance around the house. It is no surprise, then, that wasp trouble peaks in late summer. Both species build large paper nests: the bald-faced hornet builds above ground, in trees and shrubs, while the yellow jacket builds underground in repurposed cavities such as old chipmunk dens. Bald-faced hornets often occur in close proximity to homes, and even large ones seemingly appear out of nowhere because they blend in so well.

Here is a Medlock-built bald-faced hornet nest. Notice the characteristic
scalloped  pattern on the surface. These can be larger than a basketball
and house hundreds of hornets. Photo by Barbara Ladd.

Yellow jackets and bald-faced hornets can be quite aggressive and if you discover a late-season nest close to a door or walkway (or anywhere it may be disturbed by people or pets), it is wise to destroy the colony preemptively. Pest control companies handle these calls routinely. Hardware stores sell insecticidal spray with a long-range sprayer that allows the user to squirt insecticide from a safe distance (usually after dark, when the insects are in their nest and inactive).

Both bald-faced hornets and yellow jackets feed on nectar and insects and you may notice the location of the hive by watching adults come and go. Alas, in spite of industry warnings, operating lawn mowers as yellow jacket nest detector remains a popular summertime activity.