Human activities have a great impact on animal communities and their interactions, and those negative effects are rising fast in the present era – the Anthropocene. However, it is still poorly known how the loss of key animal groups affects ecosystem functions. One well-studied insect- plant interaction is the defence of plants against herbivores by ants. However, this interaction is usually measured on a small scale (plant or branch), focuses on a single plant species and habitat. Therefore, it is still unclear how ants control herbivory at a plant community scale and how the differences in environment modulate this process. Here, we assess the importance of ants in controlling herbivory levels on plant communities of two endangered and contrasting environments, the Atlantic Rain Forest and the Campo Rupestre (Rocky Grassland). We set up a factorial experimental design with 16 plots (80 x 80 m), divided into i) forest control; ii) forest ant suppression; iii) grassland control; iv) grassland ant suppression. To precise assess the effect of ant suppression on plant herbivory we used a BACI approach (Before-After-Control-Impact). We randomly choose five individuals (50 cm to 3 m) of the three most abundant plant species in each plot (15 plants per plot). From each plant, we collect and measured the area loss of 50 leaves before and 50 leaves three months after the beginning of ant suppression (24000 leaves in total). We sample a total of 28 plant species (12 in grassland and 16 in the forest). Over three consecutive months, we suppressed nearly 70% of ants, which causes a four-fold increase in herbivory when compared to control. This result was similar for both habitats (forest control = 0.61%; forest ant suppression= 2.21%; grassland control= 0.26%; grassland ant suppression = 1.14%). However, the overall herbivory levels were higher in forests than in grasslands. Here we showed for the first time that through a top-down control ants decrease substantially the herbivory on the whole plant community and this effect could be observed in a short period of time (three months). These effects seem to be more prominent in the forest than in grasslands, where plants usually present a less physical defence. By decreasing herbivory at a community level, ants can improve plant growth and ultimately enhanced carbon uptalking. Therefore, human activities that affect ant communities, especially their abundance, also impair plant community structure and ecosystem functioning, especially in forests.