Little League, school and travel-club baseball teams are not the only ones making use of baseball diamonds these days.
Some fields are also home to Cerceris fumipennis, a native, non-stinging wasp that bores brood nests into the ground to lay lay its eggs on the beetles it traps and brings to the lair. To look casually at a field, you could easily overlook the tell-tale signs of cerceris wasps — small volcano-shaped eruptions from the ground with larger holes in the center.
Turns out these beetle-gathering wasps are scientists’ biosurveillence allies in keeping track of beetles in an area — both the good ones and the bad. And, with North Carolina officially joining the ranks in 2013 of states with the highly destructive emerald ash borer, interest is strong in knowing what types of beetles cerceris wasps are capturing, said Whitney Swink, an entomologist working in the NCDA&CS Beneficial Insects Lab. To date, only Connecticut has been successful in identifying emerald ash borers using the cerceris wasp, but other states are operating similar programs to North Carolina’s in an effort to keep watch for the movement of the emerald ash borer.
“When it comes to destructive beetles, the wasps could locate beetles long before we would notice tree decline. So the hope is we would be able to save trees before they had too much damage,” Swink said.
On a recent sunny summer morning, Swink visited a Louisburg ball field to check wasp activity at the site. Swink and a co-worker had previously identified the field as a good, active site with around 60 easily detected nests. Using bright pink flag markers to note the brood nest sites, Swink waited and watched for the wasps to return to their nests carrying beetles.
Armed with a flowing, butterfly-style net, Swink walked back and forth between the first- and third-base sidelines watching for wasp activity. And it wasn’t too long before her efforts were rewarded. With a well-practiced swipe and twirl of the net, Swink hauled in a wasp with a paralyzed beetle. Before releasing the wasp, Swink carefully measured and wrote down information about the capture, depositing the beetle in a plastic bag to be examined at more length in the lab.
On one side of the field, Swink placed small, rectangular, yellow plastic pieces with holes over the nests. With stones to hold them in place, these served as collars for the nests, allowing enough room for the wasp to enter the nest, but not enough room for them to also take in beetles.
Knowing when a flying wasp was carrying a beetle requires a well-trained eye.
“They have a specific flight pattern, so once you know what they look like, then it is easier to spot them,” she said.
The wasp tends to curl its tail inward and bob up and down close to the ground, she explained. When they are trying to get their bearings to their nests, they tend to fly higher in the air and circle around the site.
While there is a good deal that is known about the wasp, there is still plenty more to discover.
“Our basic understanding is that the adults live six to eight weeks,” Swink said. “When the wasp finds a beetle, she’ll paralyze it and take it into her brood nest and she’ll lay her eggs on it. Her brood will actually kill it after they hatch. Once a female lays as many eggs as she is going to, she plugs up the entrance to her nest. At the end of their flight season, we sometimes find the female dead in the entrance.”
And there are other unexplained behaviors.
When it comes to beetles, the wasps tend to collect all sizes of them, so there is not one particular type they are partial to.
“We don’t know how they find the beetles, whether it’s by sight, by smell, by sound or from some characteristic of damaged trees,” she said. Also, these insects are not known to be social, but Swink has noticed the wasps returning sometimes in clusters, leading to some funny moments in capturing the wasps. “A bunch of them will come back all at once with beetles and I’m running around all over the place trying to collect them.”
One of the interesting aspects of the biosurveillence program is the “Adopt a Colony Program,” where community members can volunteer to monitor a site.
Volunteers will check a site once a week for five to six weeks and then send in their beetles to the lab, Swink said. Most sites are in Western North Carolina, but there are some in the East, too.
If you are interested in volunteering or learning more about the program, contact Swink at 919-233-8214 or by email at email@example.com.