With their unique colony structure, competition between ants (Hymenoptera: Formicidae) can be particularly intense, with colonies potentially willing to sacrifice large number of individuals to obtain resources or territory under the right circumstances. In this review, we cover circumstances in which ant competition escalates into combat, battle strategies and tactics, and analysis methods for these battles. The trends for when colonies choose to fight can vary greatly dependent on the species and situation, which we review in detail. Because of their large group sizes, ant conflicts can follow different patterns than many other species, with a variety of specialist adaptations and battle strategies, such as specialized worker classes and the need to rapidly recruit large number of compatriots. These same large group sizes also can make ant fighting amenable to mathematical analysis, particularly in the context of Lanchester\'s laws that consider how total numbers influence the outcome of a confrontation. Yet, dynamic behavior can often disrupt idealized mathematical predictions in real-world scenarios, even though these can still shed light on the explanations for such behavior. We also systematically cover the literature on battles between groups of ants, presenting several other interesting studies on species with unique colony organization, such as army ants and leafcutter ants.

UNASSIGNED: Social parasitic ants exploit the colonies of other ant species, either permanently or temporarily. The permanent parasites are amongst the rarest species of ants, although their hosts may be very common. Due to their rarity and often restricted distribution range, most of them are listed as vulnerable. Filling in the gaps in geographical and host ranges will advance our understanding of the social parasitic lifestyle\'s origin and evolution.
UNASSIGNED: This study reports the first records of the slave-makers Myrmoxenusalgerianus (Cagniant, 1968) for Europe (Italy, Sicily) and M.ravouxi (André 1896) for Albania and the inquiline Anergatesatratulus (Schenck, 1852) for Malta (Gozo). We also report new localities of Camponotusuniversitatis Forel, 1890 for Albania and Myrmoxenusgordiagini Ruzsky, 1902, M.kraussei (Emery, 1915) and Anergatesatratulus for Bulgaria. Diversity, type of parasite-host relationships, host range, distribution and conservation of social parasitic ant species in Bulgaria are discussed. Although social parasitic ants are still understudied in Bulgaria, they represent 21% of the regional ant fauna.

This paper provides a taxonomic revision and a review of the biology for the 10 species of North American seed-harvester ants in the genus Veromessor. Two new synonomies are proposed: V. julianus subsp. clarior W.M. Wheeler and Creighton 1934 new synonym and V. julianus subsp. manni W.M. Wheeler and Creighton 1934 new synonym are synonomized under V. julianus (Pergande, 1894). One new species is described: V. pseudolariversi new species (worker, queen, male), as a result of splitting V. lariversi Smith into two species based on morphological and genetic differences. We also diagnose previously undescribed queens and males for the following species: V. andrei (male), V. chamberlini (queen, male), V. chicoensis (queen, male), V. julianus (queen, male), and V. stoddardi (queen, male). Information on biology of each species is summarized, along with distribution maps and keys to workers, queens, and males. We then discuss the biology for species of Veromessor, focusing on several morphological and ecological traits that display strong variation across the relatively low number of species (10) in the genus. Morphological traits include degree of psammophore development, propodeal spine length, eye size and structure, and worker polymorphism and worker body size, while ecological traits include colony size and foraging method, seasonality of mating flights, mating frequency, and queen size and colony founding strategy.

The enigmatic tenebrionid genera Rondoniella Kaszab, 1970 and Durandius Kaszab, 1970 are briefly reviewed and diagnosed. Rondoniella hosoishii sp. nov. is described based on specimens collected from a nest of the arboreal ant Crematogaster sewardi in Cambodia. Because of where R. hosoishii sp. nov. was collected and its specialized morphology, the members of Rondoniella and its close relative Durandius are considered to be myrmecophilous, as was suggested in the original description. They also have reduced mouthparts, which are unknown in other tenebrionids, and they might receive food from ants by trophallaxis.

This paper reports on six species of the genus Cosmolaelaps (Laelapidae) in Russia: Cosmolaelaps lutegiensis (Shcherbak) collected from soil-litter, C. chianensis (Gu) and C. rectangularis Sheals, 1962 from Myrmica sp. (Formicidae), and Cosmolaelaps lasiophilus Joharchi sp. nov., Cosmolaelaps latisetis Joharchi sp. nov., and Cosmolaelaps sejongi Keum et al. from Lasius spp. (Formicidae). Two new species are described and illustrated from adult females and supplementary descriptions of three other species are presented to facilitate species delimitation. In addition, an identification key to all known Russian species of the genus is presented.

The arboreal ant genus Tetraponera is widely distributed in the Paleotropics. Five species groups were previously recognized in the Afrotropical region (including Madagascar), and two of these were revised. This paper provides a taxonomic treatment of the remaining species. A survey of the T. allaborans group on the African mainland leads to the recognition of fourteen species: T. clypeata (Emery) (= T. braunsi (Forel) syn. nov.); T. continua (Forel) (= T. claveaui (Santschi) syn. nov.); T. cortina sp. nov.; T. dispar sp. nov.; T. emeryi (Forel) (= T. braunsi durbanensis (Forel) syn. nov.); T. exactor sp. nov.; T. furtiva sp. nov.; T. gerdae (Stitz); T. liengmei (Forel); T. mayri (Forel); T. pedana sp. nov.; T. penzigi (Mayr) (= T. scotti Donisthorpe syn. nov. = T. zavattarii (Menozzi) syn. nov. = T. penzigi praestigiatrix Santschi syn. nov.); T. pumila sp. nov.; and T. tessmanni (Stitz). A full revision of the Malagasy species of the T. allaborans group is deferred, but the following new synonymy is established: T. hysterica (Forel) = T. hysterica inflata (Emery) syn. nov.; T. longula (Emery) = T. sahlbergii deplanata (Forel) syn. nov.; T. mandibularis (Emery) = T. flexuosa (Santschi) syn. nov.; T. morondaviensis (Forel) = T. arrogans (Santschi) syn. nov. = T. demens (Santschi) syn. nov. = T. hysterica dimidiata (Forel) syn. nov.; and T. sahlbergii = T. sahlbergii spuria (Forel) syn. nov. = T. plicatidens (Santschi) syn. nov. In the T. ambigua group the following synonymy is reinstated (syn. rev.): T. ambigua (Emery) = T. erythraea (Emery) = T. bifoveolata (Mayr) = T. angolensis Santschi; and T. ophthalmica (Emery) = T. unidens Santschi. A new species is described in the Madagascar-endemic T. grandidieri group: T. elegans sp. nov. Scrutiny of the T. natalensis group indicates the occurrence of ten species: T. andrei (Mayr), T. anthracina (Santschi), T. caffra (Santschi), T. insularis sp. nov., T. kosi sp. nov., T. mocquerysi (Andr), T. natalensis (F. Smith), T. redacta sp. nov., T. schulthessi (Santschi), and T. setosa sp. nov. T. insularis is known only from Madagascar, while the other nine species are confined to the African mainland. The following new synonymy is proposed for the T. natalensis group (senior synonym cited first): T. anthracina = T. poultoni Donisthorpe syn. nov. = T. triangularis (Stitz) syn. nov.; T. mocquerysi = T. mocquerysi biozellata (Karavaiev) syn. nov. = T. mocquerysi elongata (Stitz) syn. nov. = T. emacerata (Santschi) syn. nov. = T. triangularis illota (Santschi) syn. nov. = T. ledouxi Terron syn. nov. = T. lemoulti (Santschi) syn. nov. = T. mocquerysi lepida Wheeler syn. nov. = T. monardi (Santschi) syn. nov. = T. emacerata oberbecki (Forel) syn. nov. = T. emacerata odiosa (Forel) syn. nov.; and T. natalensis = T. angusta (Arnold) syn. nov. = T. capensis (F. Smith) syn. nov. = T. natalensis cuitensis (Forel) syn. nov. = T. mocquerysi lutea (Stitz) syn. nov. = T. natalensis obscurata (Emery) syn. nov. = T. prelli (Forel) syn. nov. = T. natalensis usambarensis (Forel) syn. nov. The extensive synonymy under T. mocquerysi and T. natalensis reflects the conviction that previous taxonomists underestimated the extent of intraspecific variation in these taxa, but further study and testing of this conclusion is warranted. An illustrated worker- and queen-based key is provided for all species of Tetraponera occurring in Africa and Madagascar, except the Malagasy members of the T. allaborans group.

Risk assessments are fundamental to invasive species management and are underpinned by comprehensive characterization of invasive species impacts. Our understanding of the impacts of invasive species is growing constantly, and several recently developed frameworks offer the opportunity to systematically categorize environmental and socioeconomic impacts of invasive species. Invasive ants are among the most widespread and damaging invaders. Although a handful of species receives most of the policy attention, nearly 200 species have established outside their native range. Here, we provide a global, comprehensive assessment of the impacts of ants and propose a priority list of risk species. We used the Socioeconomic Impact Classification for Alien Taxa (SEICAT), Environmental Impact Classification for Alien Taxa (EICAT) and Generic Impact Scoring System (GISS) to analyze 642 unique sources for 100 named species. Different methodologies provided generally consistent results. The most frequently identified socioeconomic impacts were to human health. Environmental impacts were primarily on animal and plant populations, with the most common mechanisms being predation and competition. Species recognized as harmful nearly 20 years ago featured prominently, including Wasmannia auropunctata (little fire ant, electric ant), Solenopsis invicta (red imported fire ant), Anoplolepis gracilipes (yellow crazy ant), and Pheidole megacephala (African big-headed ant). All these species except W. auropunctata have been implicated in local extinctions of native species. Although our assessments affirmed that the most serious impacts have been driven by a small number of species, our results also highlighted a substantial number of less well publicized species that have had major environmental impacts and may currently be overlooked when prioritizing prevention efforts. Several of these species were ranked as high or higher than some of the previously recognized \"usual suspects,\" most notably Nylanderia fulva (tawny crazy ant). We compared and combined our assessments with trait-based profiles and other lists to propose a consensus set of 31 priority species. Ever-increasing global trade contributes to growing rates of species introductions. The integrated approaches we used can contribute to robust, holistic risk assessments for many taxa entrained in these pathways.

Altruism is defined as an action that decreases the lifetime direct fitness of an actor and benefits one or more recipients. This phenomenon, which is generally difficult to understand and explain, requires special research attention. The subject of this review, rescue, is a type of altruistic behavior in which the actor puts itself at risk to save another individual, the recipient, that is in danger. The highest numbers of published empirical works have been devoted to rescue behavior in ants and they have enormous potential for further study. We review studies devoted to the subject and group them into four main areas of research on ant rescue actions: (1) variation in rescue behavior activity on a between-individual scale, (2) factors contributing to the evolution of rescue behavior on a between-species scale, (3) rescue behavior releaser signals and (4) rescue behavior benefits and costs. We highlight the progress in research on rescue behavior in ants, indicate that this behavior is probably much more common than previously thought yet thus far demonstrated in only a few species, and uncover research gaps and open questions that remain unexplored. We additionally point out some gaps in knowledge that become evident when research devoted to rescue behavior in rats, the second most studied group of animals in this context, is briefly overviewed. We hope to help navigate among studies on rescue behavior and provide the most up-to-date summary of the relevant literature. Moreover, we hope to encourage and facilitate researchers in behavioral ecology and other subdisciplines to further experimentally analyze rescue behavior, not only in ants but also in other taxa.

A characteristically bicolored ant belonging to the Temnothorax sordidulus species-complex is described from mountainous habitats in Iberia and named T. estel sp. nov. Three additional and closely-related taxa are newly recognized as members of the complex, including the Iberian endemics T. ibericus (Menozzi, 1922) and T. platycephalus (Espadaler, 1997) and the Pyrenean T. conatensis Galkowski Lebas, 2016. The taxonomy of all four species is reviewed and discussed within the Palearctic context. Images and an identification key are provided.

UNASSIGNED: Strongylognathus Mayr, 1853 is a Palaearctic genus, comprising 25 ant species and one subspecies, all permanent social parasites, infesting colonies of various species of Tetramorium Mayr, 1855. They have patchy distribution throughout their areas and most of them are very rare and listed as vulnerable.The taxonomy of the Strongylognathus huberi group needs thorough revision and the results presented below can be considered as preliminary.
UNASSIGNED: Four species of the socially parasitic ant genus Strongylognathus (S. karawajewi Pisarski, 1966, S. huberi dalmaticus Baroni Urbani, 1969, S. afer Emery, 1884 and S. italicus Finzi, 1924) are recorded for the first time from Bulgaria and, together with the previously-known S. testaceus and S. bulgaricus stat. rev., their total number reaches six. The taxonomic position and geographic distribution of all species are discussed and a Key for their identification, based on worker caste, is compiled.