Silverfish are very primitive creatures. They molt throughout their lives and have been found to eat dead insects and hair, as well as glue and leather.
We swat flies on our windowsills. Watch ants scramble for the crumbs on our kitchen counters. Bathe our pets to rid them of fleas. And all of us have crossed paths with the nasty cockroach.
But what most of us don’t know is that our homes are filled with a profusion of insects and their relatives, collectively called arthropods, most of which we never see.
In the summer and fall of 2012, I embarked on a postdoctoral study with a team of fellow entomologists from the North Carolina Museum of Natural Sciences and North Carolina State University to discover what arthropods can be found in our homes. It was the first comprehensive study of its kind, with the aim to uncover what people could expect to find, and why they might be there.
From the attic to the basement, ceiling to floor, we collected over 10,000 specimens — dead or alive — in 50 houses (volunteered by the public) within 30 miles of downtown Raleigh, N.C. Homeowners were surveyed and extensive notes were taken at each location.
Our team, led by Michelle Trautwein from the Museum of Natural Sciences and Rob Dunn and Matthew Bertone from North Carolina State, organized, sorted and identified the collected specimens to the family taxonomic level (or further when possible) at the museum’s Biodiversity Laboratory. Processing was time-consuming and intricate, often requiring the identification of a piece of leg or broken wing.
Ladybugs, like this Harmonia ladybug, can become nuisances in homes. They may bite and can cause skin rashes.
Our initial results were surprising: as many as 100 or more different species of arthropods were often found in a single house.
As entomologists we reveled in cataloging this relatively unexplored frontier of urban biodiversity. Within the phylum Arthropoda, most of our specimens belonged to class Insecta. But there were also arachnids (spiders and their relatives), myriapods (centipedes and millipedes) and crustaceans (generally consisting of isopods, also known as pill bugs or roly-polies) – indeed, nearly 300 families and an estimated 750 species.
Over all, arthropod groups with the most diversity in houses were flies and beetles (with over 40 different families collected), followed by ants and wasps, spiders, stink bugs and relatives, book lice, moths, isopods, millipedes, springtails, silverfish and cockroaches. Many arthropod families were collected as singletons – one species of a family collected one time in one room in one house.
Several families were found in more than 90 percent of homes: gall midges (Cecidomyiidae), ants (Formicidae) and carpet beetles (Dermestidae), along with cobweb spiders (Theridiidae), dark-winged fungus gnats (Sciaridae), cellar spiders (Pholcidae), scuttle flies (Phoridae) and book lice (Liposcelididae). Most houses also had dust mites (Pyroglyphidae).
The good news is that most of these species are harmless, living with us in harmony or at least unnoticed. Many are even doing our dirty work. Carpet beetle larvae are busy eating dead insects, spilled dog food, even our nail clippings, while dust mites are like tiny vacuum cleaners, eating the dead skin cells on our floors and in our beds.
The smokybrown cockroach is not good at surviving in homes, which explains why they are often found dead.
Some curious discoveries included spitting spiders (Scytodidae, found in 10 percent of homes), which spit a venomous silk on prey up to two centimeters away, and ant-loving crickets (Myrmecophilidae) only a few millimeters in size found in five different kitchens that also had ant infestations. We also observed nature in action: a parasitic wasp hatching out of true bug’s egg; a leaf-footed bug with a fly egg glued to its head that, if allowed to hatch, would have eaten its host alive; and flesh flies (Sarcophagidae) emerging from a cat’s recent rodent kill.
As much as we were surprised by what we did find, we were also surprised by what we didn’t find or found in very small numbers: no bedbugs, only a few German cockroaches, and just one black widow (residing in a basement).
An unexpected finding from our study is that book lice lived in just about every house. Recent molecular analyses, including research by Kevin Johnson at the Illinois Natural History Survey, have shown that book lice and head lice are more closely related to each other than previously thought. Together with bark lice, they are now joined in a single order, Psocodea. Our findings suggest that different lice are likely here to stay, whether parasitically living on our scalps in the perfect itchy storm or benignly eating mildew from our old books. As a parent who has experienced the head lice battle, I’ve come to the realization that I just have to accept there is no escaping these arthropods.
Indeed, we can conclude that having a diversity of insects and other arthropods in our homes is the norm, and there’s not much we can do about it. Plenty of houses that were sprayed regularly to kill pests still contained a wealth of arthropods. No homes were bug-free. Far from it.
Insects live near us, with us and on us, innocuous roommates in our urban dwellings – a veritable natural history museum in our homes.
More about the bugs in your home and emerging results from this study are at YourWildLife.org.