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The state of Maranhão, located in northeastern Brazil, comprises three biomes: Amazonian, Caatinga, and the Cerrado. To date, 99 ant species have been recorded in the literature from the state. In the present work, we provide for the first time a profile of the ant fauna in the state based on data from the historical literature and Brazilian institutional collections. The updated records on ant diversity for the state of Maranhão revealed a total of 279 species, belonging to 71 genera and 10 subfamilies. In total, 180 species are recorded for the first time in the state, of which four species recorded for the first time in Brazil. In summary, apart from documenting the ant fauna of the region, these results provide a basis for further studies and may contribute to future conservation efforts for the biomes present in this complex landscape.

The increasing anthropogenic pressure on the Eastern Amazon makes the diagnostic of forest degradation imperative, particularly, the effect on key communities within the riparian ecosystems. Formicidae is commonly used in diagnostic and monitoring studies in areas under restoration. This study aimed to determine the impact of riparian forest successional stages (open areas, and, early, intermediate, and advanced succession) on the richness, frequency, and composition of Formicidae. Sampling was performed during both dry and wet seasons, with the TSBF (Tropical Soil Biological and Fertility) method. Collected organisms were identified to species and morphospecies level and the analysis of collector curves determined the method efficiency to represent the ant sub-community. Ant richness and frequency were submitted to generalized linear mixed models to evaluate the effects of season, local, and successional stage. We used linear regressions model to investigate the relationship between richness and frequency of ants with canopy cover and vegetation height. Species composition was represented by the Jaccard similarity index. In total, we observed 1940 individuals grouped into 86 (morpho)species. Analysis of sampling effort suggested that we obtained more than 80% of the probable species richness. Frequency and richness significantly increased following the advanced succession in comparison with the open areas during the dry season. Canopy cover and vegetation height seemed to moderately affect both richness and frequency of Formicidae during the dry season. Intermediate and advanced succession areas presented similar composition with 50 shared species, followed by the areas of early succession with 43, and, anthropic use with 34 shared species. We conclude that the elimination of riparian forests results in a substantial effect on the richness and frequency of Formicidae, with minimum values in open areas during the dry season. Forest areas transformed to agricultural systems suffered losses of 41% and 56% of richness and frequency respectively. Succession restores forest structure and functions thus, favoring re-colonization of ant species. Formicidae reflects forests degradation, and is a key group in monitoring programs for the conservation/restoration of local riparian forests. Agroforestry and silvopastoral systems should be promoted as low impact practices for adjacent lands to riparian forests.

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