A RECENT STUDY called “Arthropods of the Great Indoors” sealed it for me: We are not alone. No, not even on that rare evening when the family’s out and you’re settling in with your favorite snack food and the just-released season of some streaming video…you’ve got company, and lots of it–like flies and spiders, beetles and ants. Mostly unseen, perhaps, but company nonetheless.

Maybe because my name is Roach, or because I live in a very old house in a rural area into which I stuff a ridiculous number of plants each winter after summering them outdoors, bringing many other living things in along with them…for whatever reason, in January I was delighted and fascinated reading the new study. It was published by entomologists at North Carolina State University, who surveyed homes in or near Raleigh, to try to get some sense of just how diverse their indoor microbiomes might be.

Wait till you hear. We are talking an average of 90-plus different arthropod types per home.

The study is called, “Arthropods of the Great Indoors: Characterizing Diversity Inside Urban and Suburban Homes,” and its lead author, Dr. Matthew Bertone, took me though the insights. We talked about stink bugs and lady beetles, spiders and fruit flies—and even what in the world a silverfish is.

Read along as you listen to the March 28, 2016 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

insects in our homes, a q&a with dr. matthew bertone

Q. First: When you’re not ID’ing arthropods in local homes [laughter], can you tell us what your role at NCSU is?

A. My job is actually to identify arthropods from homes [laughter] and also from plants out in gardens, and from commercial buildings. Any type of critter that needs to be identified, I do. We have a clinic where you can send in sick plants, and we can see whether there is an insect or something else that is affecting it.

Q. OK, I’ll be mailing you….[laughter]. No, I’m teasing, I won’t be mailing you a million things. I guess maybe when I said first tell us that, I should have asked even before: Can you explain what arthropods are? I suspect some organisms that make their way to your lab are not arthropods.

A. Arthropods are a group of invertebrates that have a number of characteristics including a hard exoskeleton, jointed legs and body in segments. So this includes familiar thing like insects, spiders, scorpions, ticks, centipedes, and even some things we like to eat from the ocean like crabs and lobsters and such. Things like worms and slugs are not arthropods.

Q. The study: What did you do, and how it was different from past studies—or were there past studies on the subject?

A. I don’t think there were any past studies that looked at this overall diversity, and none that sampled as thoroughly as we did, I think. Really there have been a few studies that use small sampling techniques, or focused on one pest species in apartments or something like that. But we decided that we wanted to go into freestanding homes all around  the area, and basically we went into the homes—trained entomologists—and surveyed each and every room, and crawled around and looked around and sampled every single arthropod we could find, dead or alive.

Q. So you just used the words, “pest species,” that some past studies focused on that. It’s an important difference, because that’s where most of the data has been up till now—like about termites, that people regard as pests and an industry has sprung up around. But this research wasn’t just those, was it?

A. People are interested in knowing more about pests, because they are affecting our lives, and we want to know how better to control them and understand them in our homes.  But this study we focused on every arthropod; if it was an arthropod, we counted it. It didn’t have to be a pest.

It didn’t even have to be living in the home the whole time. In fact, many of the specimens we collected were just accidental invaders, or just stopping by, and if they didn’t make it out of the house, they died. And so we basically identified the diversity of everything we could find.

Q. Did you test-drive this in your own homes, you and your entomologist colleagues? How did you figure out the protocol—by doing it in your own homes first?

A. We had a number of people close to us—scientists—who volunteered their homes as well as the public.  We sampled my home. The first home we sampled was kind of the test run, and we did a pretty good job of it, but we learned a few things—like that we needed knee pads, because we were crawling around a lot on hard surfaces and our knees were screaming at the end.

Q. [Laughter.]

A. Unfortunately, my home did not have as much diversity as the other homes, and I don’t know why, but still we enjoyed doing that.

Q. When you set out to do this, did you have a guess at the number of species—maybe it’s not literally species, but the diversity you’d encounter? Did you have a guess, or an office pool? [Laughter.]

A. This wasn’t very hypothesis-driven, so we didn’t have a hypothesis at first, to say, “We think there are this many species.” We had an idea of what organisms would be living in homes, or could be, or that we would find in homes maybe, if we had to guess. But we kind of went into this blind and were really concerned with just seeing what we found—kind of an exploratory study.

We had no idea that we would collect the over 10,000 specimens that we did, and such diversity.

Q. Ten-thousand specimens in just 50 free-standing homes?

A. At least 10,000 specimens, and we also did not survey for abundance, so we were looking only at diversity and didn’t count every specimen. We had at least 10,000, possibly much more.

Q. And the range of species—again, I’m not sure if I’m using the word species correctly here, was it morphospecies? What did you call them?

A. We did call them morphospecies, because a number of groups are very difficult to identify, even if you have a perfectly nice specimen. Other specimens were just a head, or something else that we knew was different from what else was in there, but we couldn’t tell what species it was.

Basically morphospecies are kind of a way to estimate. Because I was doing the identifications, I think they were pretty close to what you might estimate. Basically we found at least 579 morphospecies across the entire study, probably more—that’s a very conservative estimate. And we found a conservative average of 93 morphospecies per house.

Q. Per house; that’s amazing. And not if it were my house, which is like a zoo [laughter]. That’s fascinating. What was the majority of this diversity—what groups of arthropods were best represented?

A. Like I said, a lot of these specimens were accidental arthropods, but there was a core group that we know live in homes, and we were surprised to see how abundant they were—how many rooms they were present in. Again, we didn’t count the number of individuals. We can say yes or not it was in a room.

The groups that were most common and diverse were flies, then spiders, beetles, then wasps, and a couple of other groups trailing off from there. Some of the groups were just not as diverse; there was maybe only one or two species (and we made note of the species really well).

Basically some groups, like cobweb spiders, were found in 100 percent of homes and 65 percent of rooms. Carpet beetles also are well-known to live in homes; we found them in 100 percent of homes, and over 50 percent of rooms.  In fact lately, because it’s springtime, I have been seeing the adults in my home now. This is when people may notice them more but they’re got the larvae living then as well.

Q. What about ants? When you say “wasps,” is it wasps and their kin? Are ants in there?

A. Ants made up the largest proportion of the Hymenoptera, the true wasps, bees and ants. Ants themselves—the family—were found in 100 percent of homes, I think, and were very common. Of course they don’t live their entire life in the home—unless it’s carpenter ants, that are living in the structure of the home. Otherwise these ants are nesting outside, close by, and scouting out and entering the home for food and water.

Q. So you’re starting to get to the “why are they in our homes?” question. Some as you said were just passing through and got trapped. They weren’t living in it, the way the carpenter ants you just mentioned might be.

I found it interesting—and I love the word, which I will probably mispronounce—that these arthropods that you found are often not synanthropic. They weren’t there because they’ve evolved to find a niche living with us. Am I over-simplifying?

A. That’s exactly correct. There were a few groups like gall midges and non-biting midges that are very common out in the environment, and they’re flying around in the air, attracted to light and things. But they do not want to be in our homes—they cannot survive in there.

The gall midges, for example, are very tiny flies, a millimeter or two long. They live in plants, mostly, or a few feed on fungi or live in decaying logs. But the majority of them live in living plants—and really not even houseplants, typically, but ones out in nature. They were just flying around in the environment and happened to get inside and die, and we were there to collect them.

Above: Photographic representatives of the most frequently collected arthropod families: Twelve (12) families were represented in at least 80% of homes. For each family [the study] present[ed] the common name and percentage of homes it was found in, followed in parentheses by the scientific family name and species level identification when possible. (A) cobweb spiders, 100% (Theridiidae; shown here Parasteatoda tepidariorum (Koch)); (B) carpet beetles, 100%, (Dermestidae; shown here Anthrenus larvae); (C) gall midges, 100% (Cecidomyiidae); (D) ants, 100% (Formicidae; shown here Monomorium minimum (Buckley)); (E) book lice, 98% (Liposcelididae); (F) dark-winged fungus gnats, 96% (Sciaridae); (G) cellar spiders, 84% (Pholcidae; shown here Pholcus sp.); (H) weevils, 82% (Curculionidae; shown here Sitophilus zeamais (Motschulsky)); (I) mosquitoes, 82% (Culicidae; shown here Aedes albopictus (Skuse)); (J) scuttle flies, 82% (Phoridae; shown here Dohrniphora incisuralis (Loew)); (K) leafhoppers, 82% (Cicadellidae; shown here Sibovia sp.); (L) non-biting midges, 80% (Chironomidae). All photos by Matthew Bertone.

Q. I love bugs—though most that we’ve been talking about are not true bugs, I know. I’m not like Annie Hall calling Woody Allen in the middle of the night to kill a spider in the shower, I’m more like, “Hey, how are you? Who are you?” I wish they could talk and could talk and tell me—because I’m not so good ay keying them all out; it’s a big, diverse world.

So, I’d like to ask you about some that I see a lot in my own home, or that people ask me about. What about fruit flies—where in the world do they come from? [Laughter.]

A. They seem to show up out of nowhere; they’re a very interesting group. Since they are so small, and are very highly attuned to the smells they are attracted to, often people will be sitting outside and enjoying a glass of wine or beer, and they really like the fermenting smell.

They are different from the true fruit flies that we call the Tephritidae; those are attracted to nice, healthy fruits. But once you take the fruit of the tree and put it in that fruit basket, and it starts to decay, these fruit flies that are in the kitchens appear. Their larvae like to feed on the yeasts and bacteria that are growing on the wounded fruit, or somewhere like that. That’s why they are attracted to alcohol. The cue in on the fermentation, and eat the microorganisms.

Q. If course there is a joke among gardeners. Question: Where do tomato hornworm come from? Answer: They’re provided in every packet of tomato seeds. It seems like that, right?

A. [Laughter.] If you’re not there to see it, we’re really concerned with our own things, and we don’t see things enter. It’s not until you get a huge population or very insects that you really notice them.

Q. Spiders: the diversity in my own home (and out in the garden as well) is amazing. Sizes, shapes, patterns on their bodies, the styles of webs they weave—or don’t weave. Unbelievable complexity that could be a lifetime of fascination.

In the home, who are you finding? And do some spiders live in our homes purposefully; do they like our homes?

A. Yes, definitely. There are two general types of spiders: the web spiders, and the ground or hunting spiders. Two of the most common spider groups we found were the Pholcidae—called the cellar spiders (sometimes called daddy long-legs, though not the daddy long-legs you’d see outside), and also the cobweb spiders. Both these groups of spider live in webs, and are very common in homes. They survive for long periods. They’re very well-adapted to dry environments, and living for a long time without food. They can be opportunistic and wait for these accidental introductions or other arthropods that are living in the homes.

And then the ground or hunting spiders: They’re wandering around everywhere. They may happen into come to a hole in the home and just wander inside. They’re also pretty good at surviving, so they may make it out more often than some of the other arthropods. They will opportunistically feed on things that are in the homes, but they prefer to be outside where there is more food.

Q. I read the study in January or February, and my memory may not serve me perfectly, but I don’t think you went in cellars—basements—extensively, nor all the way into attics?

A. We went in full basements, that were easy to access, but crawl space and attics we only sampled limitedly. We wanted to keep an eye on our safety; crawling under a home, or being up in an attic over the summer is pretty brutal. So we did have a more limited sampling for those two locations.

Q. And yet all this diversity—and the reason I thought of that is we were talking spiders, and if I were to go into my attic or cellar, the diversity increases here.

A. Attics not as much as you think—it depends on where you live. In North Carolina the heat is very extreme.

Q. Yes, I am thinking of this time of year in the Northeast, when we have a lot of Asian lady beetles, for instance.

A. Those things are really overwintering, and they prefer homes as a nice overwinter site to shelter them.

As far as the basements, they’re more like caves, and have a lot more moisture and organic matter than the regular parts of the house. That does support more arthropods, things like millipedes and sowbugs, and even some molluscs (which are not arthropods), various groups that predators and other groups may feed on, that can’t survive in the home.

Q. I think I have some cricket-y things in my basement. [Laughter.]

A. The camel crickets are very common. We probably could have found more of them if we had been able to go under crawl spaces. Sometimes it’s tough to catch them from just the entrance of the crawl space.   They are very common here, and you may find them on a first floor, occasionally, or in a finished basement, but they really do like to live I that cave-like environment where they have evolved.

Q. Stink bugs—I get a lot of emails about them. And right now in my home they are all over the place. They’re appearing—and I thought they were hatching out, but maybe not?

A. Along with lady bugs—one of the major beetles that overwinter as adults—and then you get a few other groups of insects that really survive the winter as an adult.

Q. So they’re not hatching, but were dormant. Oh!

A. The bugs—stink bugs, box-elder bugs, down here we have kudzu bugs—these overwinter as adults, and in nature they would find some bark or some kind of hole in a tree or somewhere to aggregate and stay warm for the winter, even in the leaf litter. But our homes are really nice places, if they can get in, for them to do so as well.

There are also some flies—cluster flies, and a few other small flies, will do that as well.

Q. Oh, yes.

A. Even wasps—paper wasps and hornets have an overwintering queen. When it starts to warm up in the spring, people in buildings where they have been resting will start to notice a lot more of these wasps flying around.

Q. What in the world is a silverfish, because it is the most curious creature. How can it even really be a thing? [Laughter.] I have them in my cellar mostly, but sometimes they come up into the downstairs bathroom. They’re fascinating looking.

A. I like them. They’re called silverfish because they’ve got iridescent scales all over their body. They are a very primitive type of insect—a true insect, but one of the most ancient groups. They are completely wingless, and actually molt throughout their entire life, which is very different than most insects.

They have strange mating courtships, and they eat a lot of weird things. I’ve kept them in a jar with just some tissue paper as a substrate and they’ll eat holes in that. They’ll eat leather and glue. Many of them are very used to living with people. They’re harmless, but some people are a little freaked out by them.

Q. The fact that you said “primitive”—that’s how I would have described them as a layperson.

A. It’s not very scientific to say “primitive” but it’s a good way to communicate.

Q. That’s OK, because I’m not a scientist. [Laughter.] What has this study got you and your colleagues thinking about doing next? 

A. We have a lot of things lined up. We’re actually in the process of getting a paper out about the green space and some socioeconomic levels in the diversity of what we’re finding in the homes. We’re also sampling smaller subsets of homes from around the world, so we already have samples from San Francisco, from two areas in Peru (both a jungle and a city) and from Sweden. We’re going to be traveling—especially my colleagues—to other places in the world and trying to compare what we’re finding.

We’re also going to be looking at the microbiomes, the bacteria and microorganisms these things may have, that they may be moving around.

There are a lot of great research avenues looking at how these things travel between homes and in between areas of the world. A lot of possibilities.

get the whole story:

• Read the NCSU team’s study on “Arthropods of the Great Indoors.”
• Matt Bertone’s brilliant Flickr photo stream

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 28, 2016 show right here. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

(Images from NCSU study; insect photos by Dr. Matthew Bertone.)