“Start with your windowsills,” advises Rob Dunn. “Light fittings are often a graveyard, too.”
As households across the United States decorate their homes with plastic spiders for Halloween, Dunn, an applied ecologist at North Carolina State University, is encouraging people to search out the real thing — and then to photograph whatever they find, rather than squash it.
His new project, Never Home Alone, aims to gather at least 10,000 observations of arthropods — insects and their kin — from around the world. Anyone can participate, using the online nature-identification platform iNaturalist; the only condition is that the bugs must be observed indoors.
That is where humans, too, are mostly to be found. “We spend more than 90 percent of our lives inside,” Dunn said recently, citing a 2001 study funded by the Environmental Protection Agency.
In the world’s densest cities, the indoor biome is bigger than the outdoor space, at least in terms of floor area. (Indoor Manhattan, Dunn calculates, now exceeds outdoor Manhattan by a factor of 3-1.) Yet scientists know almost nothing about the spiders and flies and booklice that inhabit this space alongside us.
“There’s no shortage of papers on cockroaches and termites,” said May Berenbaum, an entomologist at the University of Illinois who was not involved in the project. “But there are hundreds, potentially thousands of house dwellers that are neutral to beneficial that we know nothing about.”
Even Dunn was, until recently, guilty of ignoring his six-legged housemates. A few years ago, he and his colleagues decided to take a census of 50 homes in Raleigh, North Carolina, including his own.
“I would have told you I had four species of spiders,” he admitted. “When we looked, we found 10 in my house — and that turns out to be the average.”
Indeed, some houses in Raleigh had more than 200 arthropod species in total; Dunn and his team have found a similar multiplicity of bugs living in homes as far afield as Sweden and Peru.
For Dunn, the domestic interior suddenly seemed more exotic than the Amazon, filled with opportunities for discovery. (Dunn’s previous surveys include studies of the microbial diversity in armpits and sourdough.) A couple of the insects he and his colleagues saw were entirely new to science, but even the named ones were deeply mysterious. In most cases, researchers don’t know what the creatures eat, what their closest relatives are or from which habitats they originally hailed.
At the same time, the extent of this ignorance was overwhelming. It took the team hours to survey a single home, and even longer to identify each specimen. At that pace, Dunn would never have enough data to understand even the basic patterns of indoor insect life, or how they differed throughout the United States, let alone the world.
iNaturalist — a citizen-science app with users across the globe, and the ability to geolocate and even identify specimens from photos using artificial intelligence — offered a way through this bottleneck.
In July, Dunn created a page for the project, and began asking the platform’s most active users to contribute. By mid-October, the project page had received more than 3,000 submissions, representing more than 800 species, from more than 1,000 participants around the world.
Already there are surprises. Take booklice: tiny light-brown bugs with fat abdomens and bulging eyes, they are neither lice nor restricted to books. They feed on starch, including the starch in bookbinding glue, but typically prefer the higher humidity of a kitchen or bathroom.
“If you were to ask any of us about booklice before this project, we would have said, sure, we’ll probably find some,” said Dunn. “So far, we’ve found them in 100 percent of houses.”
Some of the most exciting data is coming from the tropics — unsurprisingly, perhaps, given the paucity of research on indoor insects there. One particular crab spider, so named for its ability to scuttle sideways and backward, appears to be ubiquitous. In a memorable sighting, the spindly legged, fat-bodied brown spider is perched on a toothbrush, dwarfing it.
“People who live in tropical Asia clearly know this is in their houses, but it wasn’t known by scientists more generally,” Dunn said. One of the first things Dunn wants to do once he reaches 10,000 sightings is analyze how all these species are distributed globally. In Raleigh, the houses he surveyed were populated with bugs that originated in the Fertile Crescent and came to the Americas with European colonists. By that logic, Dunn would expect many of the indoor insects in New Zealand to be British. But that assumption may be wrong.
“We’ve got a whole bunch of Kiwis that have been super keen on this project,” he said. “And it turns out that there are all these endemic New Zealand indoor species, like the Wellington house spider, that I’ve never heard of.”
Other patterns are emerging, logical but intriguing nonetheless. Households with pets harbor more insect diversity; so do homes where the windows are open more often. Different bugs favor different rooms — a preference that, in some cases, seems to have been fixed for millenniums: beetle and fly remains have been used to differentiate between bathrooms and kitchens in archaeological sites from ancient Egypt to England. It’s entirely possible that certain architectural styles or floor plans favor particular insect communities, but researchers know too little to even formulate those kinds of hypotheses.
For a bug-loving scientist who wants to understand the forces shaping life’s diversity in one of the world’s fastest-growing ecosystems, the thrill of the Never Home Alone project is obvious. But for home dwellers who are more inclined to swat a fly than admire its iridescent coloring, what’s the upside? Dunn bristled at the question, before gamely pointing out that many of these species are, or could be, extremely useful.
“In tropical Asia, there’s a jumping spider that’s common in houses, and it preferentially feeds on dengue-infected mosquitoes,” he said. Spiders, on the whole, are beneficial: they feed on less pleasant insects such as roaches, earwigs, flies and clothes moths, and they rarely bite.
When we spray pesticides, we tend to kill off the beneficial spiders and speed the evolution of resistant cockroaches and bedbugs. A man in California accidentally set fire to his parents’ house while trying to kill spiders with a blowtorch.
“In my lab, we all love spiders, but, in general, I would say our attitude about these species in our houses is misdirected,” Dunn said. Effecting this attitude adjustment is perhaps the most ambitious goal of the Never Home Alone project. “Already, we’ve made connections with people we could never have reached before,” Dunn said.
He reached out to Zain Al-najm, an art student and iNaturalist contributor in Basra, Iraq, who uploaded a photo of a long-legged, thin-bodied Enicospilus wasp, its exact species unknown — the only observation on the website from this family of bugs in the entire Middle East.
“That was my most interesting insect,” Al-najm said in an email. “But where we live are a lot of creatures that we do not care about but are really amazing.”
One of the most prolific identifiers of species, Even Dankowicz, is a junior in biology at Brandeis University. Dankowicz has confirmed or corrected the identities of several hundred flies submitted to Never Home Alone.
“If you find a fly in your house, it could be a house fly,” Dankowicz said. “But just as often it’s, like, a flesh fly, a bottle fly or a cluster fly, and those are really great and interesting species that you should know about.”
Dunn accepts that most of us will never embrace the insects in our homes with great enthusiasm; he is striving merely for tolerance and, if possible, a little wonder. “Some of these species are super cool,” he said, describing a spider that kills its prey by spitting on it. (The spit is ejected from repurposed silk glands at speeds of nearly 100 feet per second).
But even without our goodwill, our insect housemates will be there; our homes, with their mild and constant climate, not to mention huge quantities of food and water, present a welcoming environment for life at all scales.
“The best we can do is hope to sway that population to species that benefit us, rather than do us harm,” said Dunn. “But first we have to understand who’s there.”
So, this Halloween, peek into those dark corners; look behind your toilet and under your bed. Resist the reflex to squash — or blowtorch — whatever you see, and take a photo instead.
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