First of all, this is for Ants.co, on the reason why we don't release ants, not even natives.
This is from an actual entomologist.
So the reason we don't re-release ants once they've been in captivity is several-fold.
First of all, let's deal with the big thing: if you buy ants from online, they're very unlikely to be local, even if they're the same species. I can buy a Lasius niger from online, which is about as abundant as you can get in the UK, but that doesn't mean I can introduce them locally. The reason for this is that local populations of a given animal have local genetics to that region. Despite being the same species, their traits can differ quite a bit between even local regions, and that, twinned with the fact that eusociality generally results in a low number of individuals within a given area (with colonies being individuals vs actual individual ants), you can seriously disrupt the local balance of genes in a given area, especially as you've released a aet of ants post-founding eliminating natural selection for a large part of their life-cycle.
But let's say you caught your niger queen from your garden, why is it important that you don't re-release? The previous argument actually still holds (you've removed them into a more febrile environment for a part of their lifecycle), but more importantly you're changing the parasitic balance of your local ecosystem.
So what the [censored] does that mean? Basically, the conditions that you raise your ants in will be very different from the native environment of the ants. As a result, parasites (mites, fungi, bacteria) are way more likely to propagate. It's not a problem for your ants cause they have an abundance of food, clean water etc., but it allows populations of these diseases to propagate in a way they wouldn't have the ability to in the wild. When you re-release, you can seriously disrupt your local invertebrate ecosystem by introducing your biological-weapon ants on it.
And it gets even worse with invasives, as those usually carry parasites the native ants are not adapted to and that will impact the remaining native ants much harder than they do the invasives that know how to deal with them.
In fact quite often the invasive species themselves aren't even the problem, but their parasites or supporting species are - this is for example true for asian river crabs in Europe, which themselves aren't causing much damage but they act as an intermediate host for a swim bladder worm that has basically already wiped out the european eel (we throw billions of young glass eel into the rivers every year but there's currently no proof that even a single one of them is able to make the journey across the ocean and back).
It is also true for Yellow Crazy ants on Christmas Island although in a reverse way - the ants themselves are a problem but the reason they can grow so out of control and are threatening to exterminate the islands native red crabs is their symbiosis with another invasive insect, an asian lac scale insect. Targeting those scale insects first is actually showing more promise than fighting the ants directly.
Generally ecosystem resilience is a very wide and complex topic. Yes, you can make assumptions on which species have a high chance to become problematic invasives, based on certain traits (ants tick literally every single box on that list) but you can never really know.
Occasionally you get species that will totally surprise you (like this totally unspectacular european herb i forgot the name of, which when introduced to Hawaii suddenly evolved lignified stems and developed into some kind of 2-3 meter high miniature tree completely taking over steep hillsides and driving out almost every other plant from this specific niche).
Solenopsis invicta - and by extent probably geminata as they are very similar - in many areas is loosing their major caste. This makes their average workers smaller, easier to accidentally be transported from one place to another by humans and even cheaper for an even higher ants-per-area ecosystem domination (and from what i've read Myrmica rubra in Canada is going for smaller workers as well). In areas they have completely taken over they are also becoming increasingly polygynous and have less flights but rely more on budding off fledgling colonies (both of these cases are what "phenoytype plasticity" means, the ability to change form to suit new environments/conditions/situations).
So technically there isn't even one type of Solenopsis invicta, there are multiple. Solenopsis geminata is likely to follow that path.
Then there's also the issue of keystone species - sometimes a predator or parasite decimating a single species central to an ecosystem can change that entire ecosystem and kick off a cascade that completely obliterates existing food chains and most of the species within it. There's an example with sea otters keeping sea urchins in check, which if the sea otters are gone basically eat up the entire plantlife that makes up the sea floor and thus collapses the whole ecosystem but the absolute best example is what happened when yellowjacket wasps got introduced to New Zealand. They didn't exactly wipe out a keystone species but they gobbled up the entirety of the honeydew a single species of the tree bark plantsuckers produced, effectively taking them out of the ecosystem and thus starving out the entire food chain right from the bottom. If nothing had been done New Zealand's woodland ecosystems would not exist today.
I consider Lasius niger a keystone ant species in central european urban and suburban environments. They absolutely dominate most inner city areas and are an effective barrier against most invasive ants, which tend to establish themselves in urban/suburban areas (or generally any area disturbed by human activity) first and then radiate outwards into more "natural" environments. If some introduced parasite wiped out Lasius niger the long-term consequences would probably be pretty bad.
In the US there was a huge panic about invasive ants in the 1930/40s which resulted in massive amounts of poison being sprayed across the landscape and it mostly killed local ants, offering the imported fire ant species an easy landgrab. Looking back, this whole campaign was a really really bad idea.
And then there's the last thing - time. The fire ant species those spanish settlers encountered just have a roughly 500 years headstart compared to the ones that are invading the southern US right now.
Yes, after a certain time every dominant invader will inevitably integrate itself into some sort of functioning ecosystem (or create one around itself, or die out), there is no question about this. The question is how many species had to go extinct to make that happen.
Even if the introduction of an invasive organism results in the complete meltdown and utter destruction of an ecosystem, given a few hundred years a new landscape will emerge and you'll hardly notice the traces of any disaster that took place.
The issue is the old ecosystem - which in case of islands specifically tends to be a very unique one with endemic species that could only be found there and nowhere else in the world - is gone, and it's not coming back. Most of the species that made it up are lost forever and those that made it may have changed beyond recognition (like the chichlids of Lake Victoria which got absolutely massacred by the intentionally introduced invasive Nil perch, causing species boundaries to break down entirely, resulting a wild array of completely unique new chichlid fish that are slowly establishing themselves into new species at the fringes of an utterly devastated ecosystem. Ironically by now the Nil perch is about to go the way of the Dodo after basically eating up the entirety of the Lake's freshwater fish population, which should send a very clear message to everyone that crap like this just isn't sustainable).
Edited by Serafine, June 15 2023 - 11:55 AM.
