The ants in NYC are changing. The most common ant in NYC is Tetramorium immigrans. These ants thrive in urban settings because they are experts at making use of windfalls like large high-calorie human trash. They like sidewalks since they are flat and warm and work well their nest building habits which would be to nest under flat rocks with sun exposure in the wild.
Despite being non-native they have been a part of the NYC ecosystem for over 100 years and other species depend on them as a food source and for their fondness for eating cockroach nymphs. (the roaches are introduced too)
However in the past two decades immigrans has been slowly displaced by a new “introduced” ant: Lasius emarginatus. Lasius emarginatus is a little larger, faster, and better at climbing. Lasius emarginatus will nest under sidewalks like immigrans but they also love flower boxes and cracks in walls.
They have not become huge house pests so the “general public” isn’t really interested as most people only pay attention to ants if they get in the way. I’m watching the change in ant populations with fascination.
It makes me a little sad to see immigrans displaced. Though, to say they are “endangered” was just clickbait. Both ants are doing just fine and finding a place in the urban ecosystem. On the one hand I see ants more often now. That’s how successful emarginatus has been, but I also see immigrans less often in Manhattan. When I see a sandwich or melted icecream on the sidewalk it’s emarginatus dominating the windfall more often.
In the Bronx immigrans is still the dominant ant. emarginatus is present but just doesn’t seem to thrive like they do in Manhattan. I wonder why.
I also think it’s interesting that we have one “invasive” displacing another. Will this happen to every city in the country? In the end I think both will persist, what will this mean for overall urban ant diversity?
One invasive species replacing another is fairly common I would think, at least on the relatively local level. In Bermuda for example, Linepithema humile replaced Pheidole megacephala in some areas, although an equilibrium of sorts has been created.
I am curious, are both of these species invasive in the ecological terms that they are harmful to the local native fauna and flora; or are they classified as just non-natives?
They are just classified as non-native. And really the term “invasive” shouldn’t be used in this case… or in any cases but the most exceptional transplanted and ecologically disruptive cases.
But, there isn’t a lot of clarity. I think most people see that hot pink (!) and think it means the creature is “bad”
The Tetramorium might have some ecological impact, but they tend to live near human residences, town parks, or cities, I don’t think they have a lot of penetration into undisturbed nature. And even where Tetramorium is found there is often substantial ant biodiversity.
Lasius emarginatus is also probably not invasive, as it has never really spread beyond the NYC metro, despite many years now of being in NYC, so I doubt its ability to invade non-urban habitats.
The ants that concern me in the northeast US are Solenopsis invicta, Brachyponera chinensis, Myrmica rubra, Myrmica ruganodis, and Nylanderia flavipes
S. invicta is one of the worlds 100 worst invasives, and is common across the southeast US, but has recently jumped all the way to Maryland, and a queen was found in NYC. Brachyponera chinensis, and Myrmica rubra are true invasives spreading in the northeast, M. ruganodis is a new introduction that may or may not become invasive like M. rubra. Nylanderia flavipes is spreading rapidly with fairly little documentation, and in theory has the ability to penetrate undisturbed forest.
The other NYC antkeepers I know theorize that they cannot survive without broadway shows and high quality bagels.
They are very successful and thrive in NYC and they seem to like the more urban parts better than places with large parks (and other ants) … I think it may be theif ants (Solenopsis molesta) that hold them back. But give them a flower box in a big plaza and they are super happy.
I see them much less often in the city, but if there is a place or park with good ant diversity they are always in the mix. But I never see big booming colonies as I do with other ants. They just get everywhere.
This is really interesting, not a lot is known about thief ants and their ecological impact, but you are not the first person to propose that they have a role in limiting invasives.
Also, it may be of note that NYC thief ants include both S. molesta and S. carolinensis
That’s what I was assuming based on how they were being talked about; but I just wanted to make for sure. I
I can agree with that. Which is why I wanted to clarify that it’s “invasive” in the non-native sense. I know that there are some species that are not technically native to an area for one reason or another but integrate into the ecosystem without harmful disruption. Definitely an interesting conversation to be had on Invasives vs non-natives species.
