Looking around the inside of your home is a very comfortable way to do some complex observations of nature. A house is a habitat not only for humans and their acknowledged cohabitating species (a wide range of mammal, reptile, bird, and fish pets) but also for many vertebrate and invertebrate species that find the non-stressful conditions of the inside of a house (not to mention the rich food sources and great nooks and crannies for reproduction and hibernation!) incredibly agreeable!
But, I don’t want to talk about the occasional raccoon that wanders into your garage or basement or the odd black snake that slithers in from the deck. We have all had birds and squirrels and bats in our attics, and I have even heard of deer pushing open screen doors and walking into living rooms and kitchens.
None of these species really “lived” in your house. They probably were frantic to get out once they realized that there were humans (probably screaming humans) way too close at hand!
Anyway, there was a research paper published in January in the journal PeerJ that looked at some more persistent fellow-occupants of our homes: the arthropods!
Mathew Bertone of North Carolina State University and his research team sampled for arthropods in fifty homes near Raleigh, North Carolina. They collected more than 10,000 specimens (on average 200 per house!) and found 34 taxonomic orders and 304 taxonomic families of arthropods. They very conservatively estimated the total number of species collected from the fifty houses at 579. On average each house sampled had 62 arthropods families and 93 species. A number of these species (149 to be exact) were quite rare and, as Bertone commented in an interview with The Atlantic magazine, “I encountered organisms I’ve never seen before as an entomologist collecting for 15 years in North Carolina.”
Most of these arthropods were not pest species. Cockroaches for example were only found in 6% of the houses, fleas were only found in 10%, and bed bugs (Cimex lectularius) were not found in any of the houses.
Species from twelve arthropod families were found in at least 80% of homes. These included “cobweb spiders” (family Theridiidae) that were found in 100% of the houses sampled , carpet beetles (family Dermestidae) also found in 100% of the houses, and gall midges (Cecidomyiidae) and ants (Formicidae) also found in 100% of the houses. There were also book lice (Liposcelididae) in 98% of the houses, dark-winged fungus gnats (Sciaridae) in 96% of the houses, “cellar” spiders (Pholcidae) in 84% of the houses, weevils (Curculionidae) in 82% of the houses, mosquitoes (Culicidae) in 82%, scuttle flies, (Phoridae) in 82%, leafhoppers (Cicadellidae), and non-biting midges (Chironomidae) in 80% of the houses. Dust mites (Dermatophagoides sp. (Pyroglyphidae)).were found in 76% of the homes sampled and significantly more mites were collected from houses that had carpeted surfaces than those that had hard surfaces (e.g., wood floors).
Four groups of arthropods dominate the average room sampled in this study: flies (23% of collected species), beetles (19%), spiders (16%) and hymenoptera (predominantly ants)(15%). Overall, there are more types of flies associated with human homes than any other group of animals. Book lice were the most ubiquitous indoor arthropod (found in 49 of 50 houses). Book lice are close relatives of the parasitic lice that have a long evolutionary history of living, among other places, in close association with birds, mammals and their nests (including those of primates).
Pest species that were collected, though, were quite typical of the same pest arthropods that have been detected in ancient archeological ruins! In other words, these species have been with us for a very long period of time! These pest species included grain weevils (Curculionidae), carpet beetles (Dermestidae), grain beetles (Silvanidae), cigarette and drugstore beetles (Anobiidae), house flies (Muscidae) and lesser house flies (Fanniidae)
This paper inspired me to do a visual arthropod scan of the rooms in my house. In the window frames of my workroom I found overwintering house flies, two very inactive earwigs, and several hibernating brown marmorated stink bugs. Up in the corners of several of the upstairs rooms I saw a number of small “cobweb” spiders and in the silk of their webs there were a number of small gnat-like flies well wrapped in spider silk awaiting their eventual ends. I have in the past found dust mites in the debris in the furnace ducts, but every other year cleaning of these ducts has greatly reduced this population (and my allergies, too!). Out on the glassed in porch I found overwintering lady bird beetles hiding under the aluminum
siding, and some more stink bugs under the carpet and in the drawers of a storage cabinet. In the basement I saw a fishing spider, several “cellar spiders,” and two “basement centipedes.” There were also a few drain flies in the basement bathroom and a few more hibernating stink bugs.
So, in a very casual, visual survey I found eleven different arthropods lurking in the corners and crevices of my house. I am far short of the 93 species average in the North Carolina study. If this were summer I know that I would add more flies (especially crane flies and several kinds of mosquito), some beetles, two or three kinds of ants, and probably a couple of kinds of moth or butterfly. Hopefully, there won’t be any fleas this year or ticks (but they almost always show up sometime in the summer!). We have, in fact, throughout the winter found the occasional deer tick on our dog. Dogs and cats are marvelous vehicles for the transport of arthropods into a house!
Finally, just to give you a little more perspective on the numbers of arthropods around us let’s look at some data from the Smithsonian Institution concerning insects (the most abundant and most diverse group of arthropods). According to the Smithsonian there are 10 quintillion (ten to the nineteenth power!!) individual insects alive on Earth at any given moment. That means for each of the 7.4 billion people on Earth there are 1.35 billion insects! Maybe we all need to add some extra rooms onto our houses to make space for all of our friends!