Lasius neglectus has 131 observations. Why?

General
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Lasius neglectus was first noticed in the 70s in Budapest, Hungary, but it was not described until 1990 I’ve been reading the original description. The authors see this ant as a spreading invasive species with anthropophilic tendencies. Neglectus can reproduce by budding and sometimes forms “super-colonies” in human environments. It is very similar to several other Lasius but instances of these ants getting into power outlets and houses made many people worry they would become a new unstoppable pest. The authors named it “Neglectus” because it could live in human garbage piles and often had “disorganized nests.”**

After reading this paper I decided to search for this ant on iNaturalist and there are only 131 observations. I expected that it would have taken over Europe or maybe the whole world by now. (The paper was very alarming) There are many papers on these ants in the following decades and I’d just like to know what happened.

First of all there is a question about to what degree this ant was even “introduced” at all. The evidence seems to point to an origin near the Black sea and from there the ant spread into Europe mostly helped by plant nurseries. (Plant nurseries who import exotic plants are responsible for many ants ending up in new places)-- at the same time some people wonder if the ant has always been in Europe and changes in human habitations and behavior simply caused populations to explode leading to alarm.

Some people will say that Lasius neglectus has been held at bay only by vigilance, ant baits and plant inspections and that the war must go on.

But there is also evidence that this ant can live on human margins without causing disruption.

But what about the small number of observations? Could it be that Lasius neglectus has taken over, and is being misidentified as other ants? I don’t think this is the case. The queens are distinctive enough that they would be caught. If the ant were booming we’d see it among the Lasius queens.

Personally I think that it is unreasonable to expect anthropophilic species to be stable when humans are not stable. People have been building and changing the world and the creatures that live closest to us will change with us. Anyway it’s an interesting and changing case. Also, how do we know that ant populations “should” remain static? (Serious question, why might they not be in a constant state of flux… and plant nurseries and human garbage just make it worse?)

The most surreal moment in my research thus far has been reading that Lasius neglectus might wipe out Lasius emarginatus in Spain. Lasius emarginatus is native to Spain but here in NYC? Not so much.

**UPDATE: I think this inference was incorrect. neglectus might better reference the way it has been ignored and neglected by taxonomy? And maybe still is? But really I did find the tone of the 1990 paper a little mean, like they just wanted to go on and on about everything wrong with the ant.

UPDATE: I’ve moved on from the 1990 type paper and now I’m reading this one from 2016 about how some of the populations have collapsed. Super interesting.

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I’m not sure this should be ruled out so easily. First of all about 90% of ant observations are workers, and those are indeed easy to misidentify. (Using the “gyne(s) present” observation field, ~9% of l. niger are, and ~12% of l. neglectus). Consider also that possibly neglectus has different swarming behaviour compared to similar species and maybe queens are out in the open at a time of day when fewer people are making observations or for a shorter time. Those are things we don’t really know.

And than I’d point out that more than a third of all neglectus observations have been recorded by just 3 people. Together with the relatively small absolute number my interpretation of this is: when someone is looking for them they find them, they are just “hidden” from people who don’t specialize in ant observations. That would also match with the literature reporting them from a bunch of countries that have 0 obs for them on inat.

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neglectus as an epithet usually means “overlooked” or not recognised until a late date. This could be either from rarity or from similarity to another species. In this instance the 1990 paper says that “The new species is named after its rather late discovery, apparently being unnoticed for some time”.

Lasius neglectus seems to be part of a species complex, also including Lasius austriacus (Austria), Lasius precursor (western Asia Minor), Lasius turcicus (Asia Minor), Lasius israelicus (southern Levant), Lasius tapinomoides (Crete) and Lasius frequens (Iran). The paper describing Lasius frequens speculates that Central Asian records of Lasius neglectus may be instead Lasius frequens.

Lasius austriacus was initially overlooked as Lasius neglectus.

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This species is one of the main subjects of my research on introduced ants. The low number of observations is most certainly a result of the difficulty of identification - for a certain identification it is necessary to see the absence of setae on scapes and tibiae, the number of occipital setae, and either be able to count the number of mandibular teeth or have a clear view of the mesosoma morphology in profile in multiple workers (still not 100% reliable). Probably over 95% of Lasius s. str. observations do not meet these criteria. Additionally, ant identifiers seem to often forget that it is an option, instead assuming that it must be a native species with a similar character combination even if neglectus cannot be excluded. It is true that the queens are somewhat more distinctive (though still easily confused), but they are rarely observed since this species does not have nuptial flights (mating happens intranidally). Hence, they are basically never seen outside the nests, unlike native Lasius spp.

However, there are also other factors. At least in the Benelux where I study this ant, it does not really keep spreading indefinitely. Instead, new populations are founded by anthropogenic introductions, and they spread rather slowly and often reach an equilibrium after some time, where the population experiences successive expansions and reductions that keep the size more or less constant over longer time periods (and sometimes populations indeed collapse as documented in the scientific literature, though the causes of this are poorly understood). Hence, its populations are very localized, though in those sites it can achieve extremely high densities. Because of this, it seems very unlikely to me that it could on its own drive a native species to extinction, especially such a common species as Lasius emarginatus.

From a human perspective, it is true that this species usually does not cause much disruption. It is a small ant without a sting and with a weak bite, which is rarely noticed unless it forages indoors in large numbers. However, from an ecological perspective it is a highly dominant species, and may potentially be extremely disruptive towards native arthropod communities, though this also needs to be studied in more detail.

Btw, there is no doubt that the species is introduced in central Europe considering this population structure which is clearly driven by anthropogenic dispersal. However, its native range is somewhat debated, currently it is thought to be somewhere in Central Asia.

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@lavateraguy one little thing - it looks like your link to a species complex is broken, as it is pointing to a local filename. Is it something like A taxonomic revision of the Palaearctic members of the subgenus Lasius s.str. (Hymenoptera, Formicidae)?:)

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Yes. I’d noticed that it wasn’t linking properly, but I missed that I’d linked to the wrong PDF, and assumed that the comma or plus sign was confusing the parser.