When you start a scientific research project, you never know what you’re going to find. Here’s one thing that Devon O’Rourke found during his Ph.D. work at UNH: “I did not suspect that so many folks were going to be that excited about picking up bat guano.”
This statement may trigger vague memories from loyal readers of this column, since I wrote about O’Rourke’s research in 2016.
It involved a cadre of citizen scientists, including my wife, who regularly collected pellets of bat poop from New Hampshire barns and mailed them to O’Rourke in Durham. His team ground them up and genetically analyzed them to get an idea on the diets of little brown bats, which often roost in barns where they deposit their droppings on the floor to be easily collected.
The project was a proof of concept for the idea that bats could act as a natural sentinel system to keep an eye out, so to speak, for invasive insects. Gather bat poop from enough places and run it through gene sequencing machines, the idea goes, and you’ll find out which arthropods are flying around at night and get advance notice the next time some plant-killing disaster of a bug migrates north.
In 2016 doing widespread poop-sampling was a novel idea to me but the pandemic has made it routine, for humans if not for bats. There is now regular genetic sampling of sewage from many places, including Concord, to keep an eye on resurgence of COVID-19. With any luck, that practice will become permanent and expand to keep an eye on many infectious diseases.
As for O’Rourke’s project, it had some predecessors. Checking the excrement of bats (and, less often, birds) for evidence of insects has been done in many places, by looking through poop with microscopes and more recently with genetic testing. But those efforts tend to target a single bug, usually a crop pest, and ignore the rest; O’Rourke’s goal was to identify every kind of bug, especially those you weren’t expecting to see.
I recently checked back with O’Rourke and his advisor, former UNH professor Jeffrey Foster, to see how it panned out, only to find that they’d just published a paper.
As is often the case with science, the initial idea didn’t entirely pan out. Part of the problem was amateur enthusiasm.
“I created a monster,” O’Rourke joked. He ended up with some 8,000 samples of various quality (that’s the drawback of using citizen scientists) taken from 20 locations in 2015 and 2016 that had to be sorted, processed and analyzed, far more than he was prepared to deal with.
In the end 899 high-quality samples were analyzed. That’s still a very good selection compared to similar studies but due to other problems, he wasn’t able to list all the specific bugs – including a lot of spiders, surprisingly – in the bats’ diet.
“We got it down to really high confidence genus level,” he said (recall that genus is the taxonomic category above species). Going further to determine individual species would require, among other things, better access to what O’Rouke called “phone books” of genetic data that could be compared against genetic strings in the guano. The problem is that those databases are often not readily available.
The research did find genetic markers from two turf and forest pests – white grubs and the Asiatic garden beetle – but the main conclusion is that little brown bats eat a much wider variety of bugs than we thought from the days when researchers had to pick through the poop with tweezers and identify insect parts.
“In light of the superior taxonomic resolution of molecular metabarcoding, historical assessments may have significantly underestimated the niche and dietary breadth of the bat species described,” is how the paper put it. (It can be seen at nature.com/articles/s41598-022-17631-z)
The paper’s title of “Spatial and temporal variation in New Hampshire bat diets” is much drier than the suggestion given by Foster, O’Rourke’s advisor.
“I wanted to call it ‘Junebugs in June’ … but they wouldn’t do it,” said Foster, who is now at Northern Arizona University and O’Rourke, who received his Ph.D. for the work, is now part of a Massachusetts startup dealing in human genomics.
Foster’s whimsical proposal reflects the fact that there wasn’t much spatial variety among the bat populations – types of bugs eaten in one place each week were mostly eaten in every place – but there was plenty of temporal variation. In other words, if you find a lot of Junebugs the sample was probably excreted in June.
Demonstrating the surprisingly eclectic culinary habits of little brown bats hints at similar variety in other bat diets. Learning that variety through similar genetic testing could be an important step in helping bat species decimated by White Nose Syndrome and habitat loss, the paper says. It could also provide some insight into changing patterns of insect populations as the climate changes.
Finally, the paper hints at the project’s original goal: “Molecular diet analyses can … leverage the bats’ expansive foraging capacity to screen for potential pests of concern. … Our results demonstrate that the broad array of arthropod orders detected using this approach can reveal pests or other non-native insects that were previously undescribed in an area.”
“This could easily be a national project,” O’Rourke said. “There’s nothing unique about our methods in New Hampshire that wouldn’t work in New Jersey or New Mexico.”
If nothing else, it could find out if everybody else likes collecting guano as much as we do.