Paying attention, again

Again?
No, it was not a good day for wasp-watching at Houghton's Pond baseball field #2.  Conscientious groundskeepers had dragged some sort of machinery over the ball fields, burying almost a hundred mama wasps in their burrows, and earning their undying enmity.*  Most mamas had not finished digging out.  I found only two beetles on the ground, and caught only two wasps carrying beetles in the air--and this in well over two hours' work. 

I have now spent over ten hours total divided between contemplating little holes in the ground, and dancing madly, lunging and swinging at flying critters.  (Actually, chasing wasps is time wasted: realizing they're danger, they begin evasive maneuvers.)

Besides doing a public service (and working on my tan lines), and without necessarily meaning to, I've become a bit of a knowledgeable observer of bare-ground ecology in general and these wasps in particular.  

 Called "velvet ants" because of their shape and covering of soft hairs, 

the many species of these wasps sport a variety of bright colors.  

In general, it's best to avoid animals with bright colors: they warn of venom.

Velvet ants are now old acquaintances.  These brightly colored insects running about the dusty ground aren't ants at all, but a very large family of wingless wasps masquerading as ants.  They aren't interested in me, and I leave them alone: the sting has earned some the nickname "cow killer."  (Best not to sit down on bare ground.)

Several other flying, running and hopping insects have caught my notice as typical residents of this habitat, though I mainly register them as "non-target species," as I go about my job. 

 You've heard of the Right Whale, so called because it was the right one for whalers to chase?

Well, this is the Wrong Wasp.  Notice the burrow is angled, and the hill asymmetrical.  (Cerceris fumipennis makes neat, vertical round holes surrounded by symmetrical hills.)

I've noticed the wasps vary widely in size, with the largest the equal of big hornets.  Why?  These beetles are, I believe, all about the same age.  The few wasps I've netted carrying beetles seem to show that big wasps catch big beetles, while smaller wasps catch smaller beetles.  (The eleven beetles I discovered abandoned outside a burrow on Monday were remarkable for their uniform size.)

 

I'm guessing these beetles were all captured by a rather small wasp.

Finally, the wasps themselves, Cerceris fumipennis aka "smoky-winged beetle bandits" are a trip.  Especially today.  They apparently navigate to their burrows at least partly by sight.  Today, emerging into a changed landscape after the groundskeepers left, the wasps spent a lot of time flying around their burrows, trying to fix their location without familiar landmarks.  They reminded me of my own maneuvers when I cannot remember where in the crowded mall lot I left my car.

 "I could have sworn I left the front door open!"

 "Yikes!  That wasn't MY front door at all!"

 "--and don't come back!"

Sometimes they get their navigation wrong.  I saw one wasp land on a burrow blocked by newly-excavated dirt.  Since these wasps push the dirt out from beneath, the blockage could only conceal a wasp already in that burrow.  The new wasp dug industriously through the blockage and entered the burrow.  Inside of three seconds she had re-emerged and taken wing, and then circled confusedly for a second or two before flying off to check her luck elsewhere.  The earlier inhabitant emerged partway, looking thoroughly put out.

The second time this happened, in a different place with other participants, I thought to make a video.  In this case, the digging wasp worked furiously without finding the hole she was looking for.  She would take a break, fly around a bit, and resume work.  I don't know what happened to her; I don't know if a wasp can start over and make a new burrow so late in the season. 

You can feel her frustration at not being able to open what she has identified as her burrow.  

She practically does head-stands trying to force an entrance, 

and has to take a flight break once in awhile.

Twice more I saw wasps try to enter burrows already occupied; I'd never seen the like before.  One of the disappointed wasps then flew down and crawled under my shoe.  When I carefully lifted it up, leaving the wasp in bright sunlight, she headed under my other shoe.  When that didn't work she crawled briefly into the shadow of a blade of grass.  From this I gather that they are drawn to dark places; and in fact the burrows are very visible when an overhead sun lights the ground and the holes stand out by contrast.

I put on my evolutionist thinking cap while leaving the field in late afternoon.

What is the "adaptive landscape" for this animal?  The wasp must dig out in spring, mate, make and maintain a burrow to protect its young, locate beetles, capture and paralyze them, lay an egg on each, and do all this while dealing with potential predators, groundskeepers, and nut-cases wielding nets.  The wasp that does any of these more successfully than its neighbors will have more successful offspring and be favored in the "struggle for existence."

Wasp size probably has big consequences.  A big wasp catches big beetles, and has offspring that have a bigger food supply, and those young probably grow into large adults.  (The adults eat, but only flower nectar, which has no protein.)  I wonder whether bigger wasps lay more eggs than smaller ones?  I wonder what the mortality rate among the young is by size class?  I wonder how small a wasp is too small to catch beetles that are big enough so wasp young don't starve?

I wonder how the peculiar hunting method of the wasp developed.  The wasp stings the beetle in  a particular place: a leg joint where the beetle's shell is thin--a chink in their  beetley armor.  I can imagine an ancestral wasp population that tried to sting beetles in a variety of places, but those that passed down in their genes a tendency to hit that exact spot had more success, produced more offspring, and spread those genes more widely in the population over time.


*Kidding about this last part.  These wasps are not vindictive: I have captured dozens, and when I release them they just go about their business, though with slightly dazed expressions. 

Jeff Michals-Brown: Wasp Watcher

Well-equipped Wasp Watcher on a baseball field:

Bag with water and sunscreen--CHECK

 Vial of alcohol (for preserving beetles, mind you)--CHECK

Indiana Jones hat set at a fashionably rakish angle--CHECK

I am now an officially trained Wasp Watcher.  I will spend a few hours each day or so from now to early August monitoring colonies of Cerceris fumipennis wasps in their preferred habitat: nearly bare, hard-packed sandy soil like that around a slightly down-at-the-heels baseball diamond. 

Why, you ask, would I want to stand in the hot sun for hours at a time watching wasps?  It's part of a nifty trick called biosurveillance.  The wasps are, in fact, working for us; and I am watching to see what beetles they bring home.

 Cerceris burrows look like ant hills with over-sized openings.

Soil is piled up evenly all around, and the hole is big enough to put a pencil in.

 

"Smoky-winged beetle bandit," wasp is the common name tentatively given to Cerceris fumipennis.  The yellowish band around the base of the abdomen is easy to spot, but not diagnostic: Cerceris fumipennis has look-alike relatives.  The real McCoy also has three yellow spots on its face.

 

You can be sure you have the right wasp when you see it enter or leave its burrow!

NOTE: the wasps are on the small side, and don't seem able to sting humans.

 

The "wrong" wasp, digging the "wrong" hole: 

notice the soil is almost all to one side.

It started for me a year ago when the majestic white ash in my back yard took sick.  Leaves yellowed and fell all summer and fall until it was bald before its time.  So I did what anyone frantic with worry would do: I turned to Google.  I quickly turned up the Mother of all ash killers: the Emerald Ash Borer.  The EAB is an invasive alien beetle from Asia which probably came into this country accidentally--like so many alien invasives before it.  It was discovered in Michigan and nearby Canada in 2002, after being imported in packing materials, probably years before.  The beetle has spread rapidly, reaching a point north of Boston just last year.  The ash trees that evolved with the EAB in Asia can usually survive an infestation, but all ash trees on this continent die.  The adult beetle eats ash leaves, causing little damage, but the beetle larva bores under the bark; the damage to the bark usually girdles the tree and kills it in a matter of months   I watched my tree anxiously for signs of beetle infestation.  The good news: my tree didn't have them; it was sick with something less serious.  The bad news: the Emerald Ash Borer was spreading unchecked, and was expected to eventually eliminate ash trees wherever in North America they were.  The EAB was recently ranked the most destructive insect in the country.  My tree, currently in the bloom of health, is doomed--so is yours.

Sadly, we have aided the Emerald Ash Borer in its spread.  On their own they might migrate a few miles in the space of a year; at that rate, we should have had many years to deal with the problem.  However, if the larvae happen to burrow into a trunk that later becomes firewood, and someone transports that firewood to another place, the beetle spreads astronomically faster.

What does the wasp, Cerceris fumipennis, have to do with this?  The wasp is a good card-carrying native, and harmless to humans.  But it is a fierce predator to certain types of beetles: those wood-borers of the family Buprestidae, called Jewel Beetles.  It stings the beetles, and carries the paralyzed insects back to its burrow to lay its eggs on.  The wasp is good at catching beetles, and Wasp Watchers are good at catching wasps.  In effect, the wasps are sampling the local beetle population, and doing it far more effectively than we can.  We need only confiscate some of the beetles to find out who's out there.  The collected beetles go on to experts who will identify them. In short, we are putting wasps to work finding us invasive wood-boring beetles.

Although the EAB isn't hard to identify, collecting all those beetles may give us an early heads-up on the next invasive--maybe early enough to eliminate or control it.  North America has already lost its chestnuts to chestnut blight, most of its large elms to Dutch elm disease, and it's rapidly losing ashes --some of the most majestic forest trees remaining.

I don't want to lose any more.

I hope to God not to find a half-inch long, narrowly oval, metallic emerald green beetle among the wasps' prey.  But if I don't find any this year, I'm sure I will next.

https://en.wikipedia.org/wiki/Emerald_ash_borer

https://en.wikipedia.org/wiki/Cerceris_fumipennis

http://www.emeraldashborer.info/index.cfm

http://cerceris.info/index.html