• Life cycle. The scarce data noted below probably do not reflect the variation to be found between populations as northern as that from Warsaw (Poland) and those from Iran. As compared with other Lasius species, the sexuals appear earlier in the year: as early as March, within heated buildings in Budapest (Andrásfalvy, in litt.). In three studied populations from NE Spain, activity throughout the year shows remarkably similar duration, beginning in early March until late November, when certain colonies in protected zones are still active. 

• Daily activity. In two Spanish populations the ants remain active for 24 h/day from May to late September, with temperature controlling the daily cycle. 

• Food. This ant seems to be highly dependent on aphid honeydew. In North-east Spain, during the early season, when leaves are still lacking on deciduous trees or tree aphids are scarce, this ant constructs earth tents over small herbs protecting stem and root aphids. In the full season ants visit aphids on different tree species in huge numbers (video: 13''; 2,58MB.View/download: 7,81MB) and in rare instances individuals are seen carrying small prey (collembola, psocoptera). Ants are active throughout the entire day and aphid tending lasts for 24 h/day, from late April to late October, imposing a non-negligible cost on the energetic budget of individual trees. Preliminary quantitative measures indicate that ants can extract a mean of 250 cc honeydew per month on holm oak (Quercus ilex) and as much as 950 cc honeydew per month on poplar trees (Populus nigra). In a recent study (Paris & Espadaler 2009) food collection performed by the invasive ant Lasius neglectus and by the native ant L. grandis was compared. The invasive ant collected 2.09 kg of honeydew per tree while the native ant collected 0.82 kg. The aphid Lachnus roboris was visited by both ant species. In holm oaks colonized by L. neglectus, aphid abundance tended to increase and its honeydew production increased twofold. The percentage of untended aphids was lower in holm trees occupied by L. neglectus. Tending ants may also prey on insects: the native ant workers carried more insects than the invasive ant. Both ant species preyed mainly on Psocoptera and the rarely tended aphid, Hoplocallis picta. We conclude that the higher honeydew collection achieved by L. neglectus was the consequence of (1) its greater abundance, which enabled this ant to tend more Lachnus roboris and (2) its greater level of attention towards promoting an increase of honeydew production. Tree species occupied in Spain.

• Sexuals physiological condition and behaviour. Nuptial flight seems to be absent. In a single instance alate males and queens were found in a spider net on a house wall (Seifert 2000: 178), although this is not a definite proof of flying behaviour. Except for this case, sexuals have never been detected flying out of the nest. Intranidal mating, thus, is probably the rule (Van Loon et al. 1990; Espadaler & Rey 2001).

• Social structure. Depending on the populations, colonies are very difficult to delimit as they may coalesce and integrate a supercolony occupying continuous areas, as large as 17 ha. In urban areas the colonies are considerably split and may ocupy a single tree and up to 3600 ha. Finding many dealate queens (polygyny) in a nest is a key diagnostic characteristic of this species, the single polygynous European Lasius (s.str.). This biological aspect is very probably the best way to identify it, although it is advisable to verify with the morphology. The number of queens depends on colony size. Queen number, estimated by queens found under stones, is about 35500 in the supercolony of Seva. Using soil cores, worker number for that population in May 2002, was estimated as 1.12 x 10⁸ (Espadaler et al. 2004). The species merits the qualification of unicolonial.

• Internest and interpopulation relationships show the usual trait already known for unicolonial ants: a reduced level of agressiveness, though some non-native populations show higher levels of aggression in lab tests. Laboratory tests on aggression should be  refined to be fully applicable to this light-avoiding ant. Have a look at its less than stressful tactics (video: 1' 17''; 3.07MB. View/download: 2.98MB) and compare with the much more aggressive Argentine ant (video: 1' 20''; 3.01MB. View/download: 2.91MB).

• Aggression levels. L. neglectus is highly aggressive against three native Iberian Lasius species (L. grandis Forel, 1909, L. emarginatus (Oliver, 1792), and L. cinereus Seifert, 1992), expressed as a higher attack rate of L. neglectus and behavioural dominance throughout the aggressive encounters. Attacks of L. neglectus were performed fastest and most frequent against L. grandis, and also the highest antennation frequencies were observed in encounters between these two species. This could be due to the largest difference in body size, or due to a greater overlap in ecological niche between L. neglectus and L. grandis com­pared to the other two native species (Cremer et al. 2006).

• Nesting habits. The areas occupied furnish a wide array of possible nesting sites: under stones, temporal refuges with aphids at the base of herbs, amid rubbish. 

• Nesting habitat. Non-native populations of this ant are usually related to human-modified habitats -ranging from purely urban habitats in streets with heavy traffic to city gardens, urban woods, small towns -or semi-urban areas.

• Colony expansion. The expansion process of a supercolony in Spain seems to be much helped by the progresive urbanization of lots. This development usually implies the cutting and burning of all natural vegetation but trees. The planting of grass and continuous irrigation of grass that follows favours the establishment of the ants. See also a map showing the area of the Debrecen supercolony (data from 1998, 2000, and 2002) . The presence of different ant species' nest entrances was mapped.  The expansion of L. neglectus was variable in space and time. It seems that L. neglectus spreads fastest on paths, and does not spread rapidly in shady and cool areas occupied by coniferous bushes. The data suggest that the relative L. niger (L., 1758) is more impacted by the invasion of L. neglectus than Tetramorium cf. caespitum (L., 1758). Moreover, Liometopum microcephalum (Panzer, 1798) and Lasius fuliginosus (Latreille, 1798) were able to defend their territory (Tartally 2006).

• A recent experimental research by Ugelvig & Cremer (2007), using L. neglectus from four populations (Bellaterra, Jena, Seva, Volterra) is the first demonstration of contact immunity in social Hymenoptera. Social contact with individual workers that were exposed to a fungal parasite (Metarhizium anisopliae var. anisopliae) provided a clear survival benefit to non-treated ants, upon later contact with the same parasite. Behaviour was also affected: brood care was absent in infested ants whereas naive nestmates increased brood-care activities. The collective behavioural and physiological prophyllaxis work to promote the immunity of the society and to counteract the high risk of disease transmission.

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