Ants represent only 1.5 % of known insect species, yet they are abundant, making up 10 % to 15 % of animal biomass in terrestrial ecosystems (^{Alonso 2000}, Rico-Gray and Oliveira 2007) and playing important roles in ecosystem processes (^{Del Toro et al. 2012}). Therefore, regional species lists, particularly of ants, are an important tool for the development of scientific research and for the creation of conservation projects (^{Lewinsohn et al. 2005}, ^{Vicente et al. 2016}). Although the ants occupy areas from the subsoil to the forest canopy, studies on the diversity of arboreal ant fauna are not so frequent in Neotropical regions, being scarce in the Amazon (^{Ryder-Wilkie et al. 2010}, Vicente et al. 2016). Thus, to contribute to the knowledge of the Neotropical ant fauna, this paper lists for the first time the arboreal ant fauna found in an Amazonian forest remnant in the municipality of Paranaíta, State of Mato Grosso, Brazil.

Understory ants were sampled in December 2013 in a forest remnant of 400ha (9°48’ South, 56°20’ West). Ants were sampled with a beating-tray method adapted in 24 points equidistant at least 25m and 200m from the edge. Then all vegetation in each point within 4m² between 1-3 meters in height was steadily shaken and the ants that fell on the canvas were collected (^{Vicente et al. 2016}). All sampled ants were identified to as to genus with ^{Baccaro (2015)} and posteriorly, the specimens were sent to specialists to confirm species identification (see acknowledgments) at the ant collection from the Museu Paraense Emílio Goeldi (MPEG) and Coleção Entomológica Padre Jesus Santiago Moure (DZUP), both in Brazil, where vouchers were deposited.

A total of 32 ant species was recorded, belonging to 18 genera and six subfamilies. The most frequent species were Azteca sp. 1 and Solenopsis sp.1 (sampled in 50 % of the samples), Brachymyrmex sp.1 (41 %), Pseudomyrmex tenuis (Fabricius, 1804) (37.5 %), Ectatomma tuberculatum (Olivier, 1792) (28 %), Crematogaster limata Smith, 1858 and Nylanderia steinheili (Forell, 1893) (22 % each species). As for the other species, each species was sampled at a maximum of 12.5 % of the samples, being: Camponotus burtoni Mann, 1916, C. latangulus Roger, 1863, C. planatus Roger, 1863, Camponotus sp.1, Camponotus sp.3, Crematogaster carinata Mayr, 1862, C. longispina Emery, 1890, C. limata, C. nigropilosa Mayr, 1870, Dolichoderus attelaboides (Fabricius, 1775), D. ghilianii Emery, 1894, D. imitator Emery, 1894, Gnamptogenys horni (Santschi, 1929), G. pleurodon (Emery, 1896), G. striatula Mayr, 1884, Neoponera inversa (Smith, 1858), N. unidentata (Mayr, 1862), Nesomyrmex aff. wilda, Nylanderia steinheili (Forel, 1893), Ochetomyrmex semipolitus Mayr, 1878, Pheidole sp. 1, Pheidole sp. 2, Pheidole nr radoszkowskii, Pseudomyrmex sp. 1, Rasopone arhuaca (Forel, 1901), Solenopsis sp. 1, Solenopsis sp. 2, Strumigenys sp. 1, Tapinoma melanocephalum (Fabricius, 1793), Tapinoma sp. 1, Wasmannia auropunctata (Roger, 1863). It is also worth mentioning that among these species sampled using the described method, G. striatula was also sampled manually in the locality nesting in an unidentified Araceae species.

Camponotus is the most specious genus in this study contributing with two of the four new distribution records. Camponotus burtoni and C. planatus were collected for the first time in the state of Mato Grosso, with C. planatus being recorded for the first time in Brazil. The other ant species that was recorded for the first time in the state of Mato Grosso was N. steinheili. This species is native to the Neotropical region, occurring from the Southeast region of Brazil (State of Rio de Janeiro) to Mexico (^{Brandão 1991}) having been introduced into other countries (^{Kallal and LaPolla 2012}, ^{Moreau et al. 2014}). The other species sampled for the first time in Mato Grosso, was Crematogaster longispina. Most of the ant species that were sampled for the first time in the state of Mato Grosso show the lowest frequencies of occurrence. Probably these ants had not been registered in the region because of their natural low abundance combined with the scarcity of studies with arboreal ants and the lack of reviews of some local taxonomic groups such as Camponotus, Crematogaster and Nylanderia.