“Super-slugs” are invading British gardens – and we don’t know how to stop them

Mmmmmm, slimy. Image: Xauxa Håkan Svensson.

The Daily Mail calls it a “slime wave”. The Sun calls them “an army”. Either way, both papers have reported 500bn slugs are set to invade British gardens, after a mild winter created perfect breeding conditions. The Conversation

So is the UK really about to be overwhelmed by slimy slugs? The simple answer is no, but there could be something far worse in store.

Headline numbers alone aren’t necessarily something to get in a lather over. A typical garden can contain several thousand slugs, and the “500bn” figure is derived from estimates of maximum numbers per area. In any case, slug numbers can rise and fall a great deal across time and space, in natural cycles, and even astonishingly dramatic increases are not always cause for concern. Like waves crashing against a beach, the rise is often transient and local – usually slug numbers will drop back to normal, with the disturbance hardly noticed beyond a few local gardeners.

What is more problematic is the progressive, sustained and perhaps less spectacular rise in numbers which, tsunami-like, is maintained for far longer, and spreads widely throughout the countryside. This is Britain’s real slug invasion. So what can we do about it?

The trigger seems innocuous enough in isolation: a few non-native slugs from continental Europe have accidentally been introduced. Several of these species have close relatives in the UK, so similar in fact that only specialists can tell them apart, and they can interbreed freely. Of course, many animals can create hybrids without presenting a threat, but what makes slugs different – and these hybrids so worrying – is their interesting and deviant sex lives.

This is a hybrid between a ‘Spanish stealth slug’ and the UK’s common black slug. Image: Les Noble/author provided.

Slugs are hermaphrodites, which means the same individual exists as both sexes; they first develop as males, before experiencing a true hermaphrodite phase to become female. This means they can dispense with normal mating requirements, and this is where the consequences of the difference between British and continental species becomes significant.

Why British slugs are different

When slugs colonised the UK after the last ice age, they found an island recently covered with ice sheets, where the biological diversity remained poorer than continental Europe. In these circumstances, the ability to self-fertilise was a good evolutionary strategy, one which ensured reproduction even when slug populations were devasated by harsh weather.

A downside of such continued close inbreeding (and mating with oneself is as inbred as it gets) is a rapid loss of genetic variability, and some British slug species eventually came to consist of almost genetically identical individuals. This meant they were more vulnerable to parasites and pathogens that could rapidly evolve to overcome their defences.

Meanwhile, in continental Europe, slugs were becoming more diverse, as balmier weather meant parasites and pathogens were a bigger issue than finding a mate. These slugs tended not to self-fertilise, and were genetically highly variable. This made at least some of them more resilient to attacks from parasites – a possibility not afforded to the inbred British slugs.

Echoes of these different past environments resonate in contemporary species. British slugs, adapted to a variable climate and dearth of mates, have fallen into the clichéd “No sex please, we’re British” mould, producing fewer, bigger eggs later in life by self-fertilisation. Continental slugs, meanwhile, adapted to resist rapidly evolving enemies. Their strategy is therefore to produce many smaller eggs earlier in life, which maximises genetic diversity and compensates for losing many individuals to infection.

The ‘Spanish slug’, one of Britain’s key invaders. Image: tviolet/creative commons.

These different adaptations weren’t an issue until humans disturbed the natural order by moving slugs back and forth as stowaways in commercial produce. As a result of this, we’ve seen widespread breeding between British and continental species. These new hybrid “super-slugs” are highly fertile, and their genetically diverse offspring are adapted to cope with both the British climate and parasites and pathogens, most of which remain in continental Europe anyway.


Fighting the slug invasion?

Legislation aimed at environmental protection has led to the EU banning commercial use of molluscicides (pelleted chemicals which poison slugs but cause collateral damage to other wildlife). Instead, the emphasis is on using natural enemies like nematode worms, though these are generally ineffective against the larger invasive hybrids.

Nonetheless, the increased slug biomass could still host important veterinary or agricultural parasites and pathogens, spreading more plant and animal diseases. Remarkably, despite their obvious presence in our gardens, we remain startlingly ignorant of the fundamental biology of slugs; evidenced by recent work which increased the number of identified British species by more than a fifth.

So where are we going with this phenomenon? Studies have already found invasive slugs and snails can destabilise ecosystems and reduce biodiversity in the US and Scandinavia. Something similar is happening here in the UK.

The good news is that our research suggests population sizes do eventually begin to decline, after 30 to 40 years. The ecosystem may eventually rebound from this slug invasion, but it remains to be seen how long it will take and what the lasting effects will be for the spread of diseases, ecosystem services, or British biodiversity.

Leslie Noble is a reader in zoology at the University of Aberdeen.

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

 
 
 
 

Urgently needed: Timely, more detailed standardized data on US evictions

Graffiti asking for rent forgiveness is seen on a wall on La Brea Ave amid the Covid-19 pandemic in Los Angeles, California. (Valerie Macon/AFP via Getty Images)

Last week the Eviction Lab, a team of eviction and housing policy researchers at Princeton University, released a new dashboard that provides timely, city-level US eviction data for use in monitoring eviction spikes and other trends as Covid restrictions ease. 

In 2018, Eviction Lab released the first national database of evictions in the US. The nationwide data are granular, going down to the level of a few city blocks in some places, but lagged by several years, so their use is more geared toward understanding the scope of the problem across the US, rather than making timely decisions to help city residents now. 

Eviction Lab’s new Eviction Tracking System, however, provides weekly updates on evictions by city and compares them to baseline data from past years. The researchers hope that the timeliness of this new data will allow for quicker action in the event that the US begins to see a wave of evictions once Covid eviction moratoriums are phased out.

But, due to a lack of standardization in eviction filings across the US, the Eviction Tracking System is currently available for only 11 cities, leaving many more places facing a high risk of eviction spikes out of the loop.

Each city included in the Eviction Tracking System shows rolling weekly and monthly eviction filing counts. A percent change is calculated by comparing current eviction filings to baseline eviction filings for a quick look at whether a city might be experiencing an uptick.

Timely US eviction data for a handful of cities is now available from the Eviction Lab. (Courtesy Eviction Lab)

The tracking system also provides a more detailed report on each city’s Covid eviction moratorium efforts and more granular geographic and demographic information on the city’s evictions.

Click to the above image to see a city-level eviction map, in this case for Pittsburgh. (Courtesy Eviction Lab)

As part of their Covid Resource, the Eviction Lab together with Columbia Law School professor Emily Benfer also compiled a scorecard for each US state that ranks Covid-related tenant protection measures. A total of 15 of the 50 US states plus Washington DC received a score of zero because those states provided little if any protections.

CityMetric talked with Peter Hepburn, an assistant professor at Rutgers who just finished a two-year postdoc at the Eviction Lab, and Jeff Reichman, principal at the data science research firm January Advisors, about the struggles involved in collecting and analysing eviction data across the US.

Perhaps the most notable hurdle both researchers addressed is that there’s no standardized reporting of evictions across jurisdictions. Most evictions are reported to county-level governments, however what “reporting” means differs among and even within each county. 

In Texas, evictions go through the Justice of the Peace Courts. In Virginia they’re processed by General District Courts. Judges in Milwaukee are sealing more eviction case documents that come through their courtroom. In Austin, Pittsburgh and Richmond, eviction addresses aren’t available online but ZIP codes are. In Denver you have to pay about $7 to access a single eviction filing. In Alabama*, it’s $10 per eviction filing. 

Once the filings are acquired, the next barrier is normalizing them. While some jurisdictions share reporting systems, many have different fields and formats. Some are digital, but many are images of text or handwritten documents that require optical character recognition programs and natural language processors in order to translate them into data. That, or the filings would have to be processed by hand. 

“There's not enough interns in the world to do that work,” says Hepburn.


Aggregating data from all of these sources and normalizing them requires knowledge of the nuances in each jurisdiction. “It would be nice if, for every region, we were looking for the exact same things,” says Reichman. “Instead, depending on the vendor that they use, and depending on how the data is made available, it's a puzzle for each one.”

In December of 2019, US Senators Michael Bennet of Colorado and Rob Portman of Ohio introduced a bill that would set up state and local grants aimed at reducing low-income evictions. Included in the bill is a measure to enhance data collection. Hepburn is hopeful that the bill could one day mean an easier job for those trying to analyse eviction data.

That said, Hepburn and Reichman caution against the public release of granular eviction data. 

“In a lot of cases, what this gets used for is for tenant screening services,” says Hepburn. “There are companies that go and collect these data and make them available to landlords to try to check and see if their potential tenants have been previously evicted, or even just filed against for eviction, without any sort of judgement.”

According to research by Eviction Lab principal Matthew Desmond and Tracey Shollenberger, who is now vice president of science at Harvard’s Center for Policing Equity, residents who have been evicted or even just filed against for eviction often have a much harder time finding equal-quality housing in the future. That coupled with evidence that evictions affect minority populations at disproportionate rates can lead to widening racial and economic gaps in neighborhoods.

While opening up raw data on evictions to the public would not be the best option, making timely, granular data available to researchers and government officials can improve the system’s ability to respond to potential eviction crises.

Data on current and historical evictions can help city officials spot trends in who is getting evicted and who is doing the evicting. It can help inform new housing policy and reform old housing policies that may put more vulnerable citizens at undue risk.

Hepburn says that the Eviction Lab is currently working, in part with the ACLU, on research that shows the extent to which Black renters are disproportionately affected by the eviction crisis.

More broadly, says Hepburn, better data can help provide some oversight for a system which is largely unregulated.

“It's the Wild West, right? There's no right to representation. Defendants have no right to counsel. They're on their own here,” says Hepburn. “I mean, this is people losing their homes, and they're being processed in bulk very quickly by the system that has very little oversight, and that we know very little about.”

A 2018 report by the Philadelphia Mayor’s Taskforce on Eviction Prevention and Response found that of Philadelphia’s 22,500 eviction cases in 2016, tenants had legal representation in only 9% of them.

Included in Hepburn’s eviction data wishlist is an additional ask, something that is rarely included in any of the filings that the Eviction Lab and January Advisors have been poring over for years. He wants to know the relationship between money owed and monthly rent.

“At the individual level, if you were found to owe $1,500, was that on an apartment that's $1,500 a month? Or was it an apartment that's $500 a month? Because that makes a big difference in the story you're telling about the nature of the crisis, right? If you're letting somebody get three months behind that's different than evicting them immediately once they fall behind,” Hepburn says.

Now that the Eviction Tracking System has been out for a week, Hepburn says one of the next steps is to start reaching out to state and local governments to see if they can garner interest in the project. While he’s not ready to name any names just yet, he says that they’re already involved in talks with some interested parties.

*Correction: This story initially misidentified a jurisdiction that charges $10 to access an eviction filing. It is the state of Alabama, not the city of Atlanta. Also, at the time of publication, Peter Hepburn was an assistant professor at Rutgers, not an associate professor.

Alexandra Kanik is a data reporter at CityMetric.