You think your house is clean – but you basically live in a zoo

A European garden spider, in a European garden. Image: Getty.

Do you take pride in a clean house? Even if you do, while they may not be obvious, but a recent US survey has shown that each of our homes harbours a fauna of perhaps hundreds of species of insect and other terrestrial arthropods such as mites, millipedes and centipedes.

The survey, conducted in free-standing houses in Raleigh, North Carolina, sampled every arthropod, both known pests and others. Almost 75 per cent of the diversity consisted of just four main groups, true flies (Diptera), spiders (Araneae), beetles (Coleoptera), and wasps and ants (Hymenoptera).

Most of the species are not the ones you might traditionally associate with houses, such as German cockroaches (Blattella germanica) and house flies (Musca domestica). Rather, they tended to be local arthropods filtered from the surrounding landscape.

More than 500 rooms were surveyed in total, and a staggering 99 per cent of them contained arthropods. Insects were overwhelmingly common, with over 90 per cent of kitchens, bedrooms and bathrooms harbouring them. The bigger the house, the more species it contained, and the human inhabitants were generally unaware of their uninvited guests.

How do these insects enter homes? Most US homes have fly screens installed on windows, but many of these arthropods are small and can enter through the gaps around doors and windows, chimneys, drains, basements, attics and ceiling spaces.

If similar studies were conducted elsewhere, they would probably uncover similar results. So what are all these mini-beasts doing in our homes?

Proportion of different arthropods found in homes: there are a lot of flies and spiders. Image: Bertone et al.

Meet the arthropods

Arthropods have been living in our homes ever since we moved out of caves and built houses. For example, the remains of a variety of beetles that consume grains are common in Egyptian archaeological sites more than 3,000 years old.

Animal domestication and food storage brought many different opportunities for arthropods to make a living where we live. Some, such as bed bugs, may have followed us out of the caves.

Most studies have focused on known pests, with particular emphasis on medically and economically important species such as mosquitoes, termites, fleas and dust mites.

The most common mini-beasts in homes (click to expand): (A) cobweb spiders (B) carpet beetles (c) gall midges (D) ants (E) book lice (F) dark-winged fungus gnats (G) cellar spiders (H) weevils (I) mosquitoes (J) scuttle flies (K) leafhoppers (L) non-biting midges. Image: Bertone et al.

The US study was the first to uncover the multitude of other non-pest species in our homes. Their true interactions with humans remain largely unknown. None is known to cause us any direct harm.

Common groups found in almost all houses included cobweb spiders (Theridiidae), carpet beetles (Dermestidae), gall midges (Cecidomyiidae), ants, book lice (Liposcelididae), and fungus gnats (Sciaridae). Dust mites and American cockroaches were found in 75 per cent of the houses sampled. Flies were found in over 80 per cent of homes, but the commonest ones (non-biting midges, Chironomidae; and gall midges, Cecidomyiidae) are harmless and form part of the aerial plankton outside homes.

Interestingly, none of the homes surveyed had any bed bugs. This suggests these insects may thrive best in motels, hotels and hostels rather than in permanent residences.

Book lice have a broad diet, including grain, fungi, paper products and organic waste, and have a long history of living in close association with birds and mammals and their nests. They can survive for long periods without food and females can reproduce without sex (parthenogenesis). Both these attributes contribute to their success.

A whole ecosystem in your living room

The insects found have a range of different relationships with people, from species that have a very strong association (for example, carpet beetles, cobweb spiders), to others that seek shelter and resources only occasionally (ants, hunting spiders), to others that blunder into our homes and are trapped to their detriment (plant-feeding bugs and gall midges).

Many of the insects found were plant feeders. The were probably attracted into the home by lights at night, or introduced via cut flowers, and cannot complete their life cycle in the home.

Some, such as the fungus gnats (Sciaridae), may be able to complete their life cycle in the soil associated with indoor plants. Some predators, such as spiders, are able to feed on other arthropods in the home, and others are tiny parasitic wasps, which may be able to complete their life cycle on other arthropods in the home. In these cases our homes may contain very simple, but self-sustaining, ecosystems.

Many of the insects found in the US homes are a sample of the local arthropod fauna that are not known to cause us any direct harm. All the pest groups in the US homes are also present elsewhere.

These results suggests that if a similar survey was conducted in an Australian city (for example), a minority of the insects would be the cosmopolitan pests found in human houses all over the world, whereas the majority would be a sample of the local Australian arthropod fauna.

Should we be worried? Probably not: other recent research has shown how diverse the arthropod fauna is in urban areas as well. If your home harbours a healthy arthropod fauna, it is safe for you as well. Whether we like it or not, we have evolved with a zoo of arthropod mini-beasts in our dwellings and suburbs for millions of years.

David Yeates is director of the Australian National Insect Collection at CSIRO.

This article was originally published on The Conversation. Read the original article.


What's actually in the UK government’s bailout package for Transport for London?

Wood Green Underground station, north London. Image: Getty.

On 14 May, hours before London’s transport authority ran out of money, the British government agreed to a financial rescue package. Many details of that bailout – its size, the fact it was roughly two-thirds cash and one-third loan, many conditions attached – have been known about for weeks. 

But the information was filtered through spokespeople, because the exact terms of the deal had not been published. This was clearly a source of frustration for London’s mayor Sadiq Khan, who stood to take the political heat for some of the ensuing cuts (to free travel for the old or young, say), but had no way of backing up his contention that the British government made him do it.

That changed Tuesday when Transport for London published this month's board papers, which include a copy of the letter in which transport secretary Grant Shapps sets out the exact terms of the bailout deal. You can read the whole thing here, if you’re so minded, but here are the three big things revealed in the new disclosure.

Firstly, there’s some flexibility in the size of the deal. The bailout was reported to be worth £1.6 billion, significantly less than the £1.9 billion that TfL wanted. In his letter, Shapps spells it out: “To the extent that the actual funding shortfall is greater or lesser than £1.6bn then the amount of Extraordinary Grant and TfL borrowing will increase pro rata, up to a maximum of £1.9bn in aggregate or reduce pro rata accordingly”. 

To put that in English, London’s transport network will not be grinding to a halt because the government didn’t believe TfL about how much money it would need. Up to a point, the money will be available without further negotiations.

The second big takeaway from these board papers is that negotiations will be going on anyway. This bail out is meant to keep TfL rolling until 17 October; but because the agency gets around three-quarters of its revenues from fares, and because the pandemic means fares are likely to be depressed for the foreseeable future, it’s not clear what is meant to happen after that. Social distancing, the board papers note, means that the network will only be able to handle 13 to 20% of normal passenger numbers, even when every service is running.

Shapps’ letter doesn’t answer this question, but it does at least give a sense of when an answer may be forthcoming. It promises “an immediate and broad ranging government-led review of TfL’s future financial position and future financial structure”, which will publish detailed recommendations by the end of August. That will take in fares, operating efficiencies, capital expenditure, “the current fiscal devolution arrangements” – basically, everything. 

The third thing we leaned from that letter is that, to the first approximation, every change to London’s transport policy that is now being rushed through was an explicit condition of this deal. Segregated cycle lanes, pavement extensions and road closures? All in there. So are the suspension of free travel for people under 18, or free peak-hours travel for those over 60. So are increases in the level of the congestion charge.

Many of these changes may be unpopular, but we now know they are not being embraced by London’s mayor entirely on their own merit: They’re being pushed by the Department of Transport as a condition of receiving the bailout. No wonder Khan was miffed that the latter hadn’t been published.

Jonn Elledge was founding editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.