Frass obtained from the production of Black Soldier Fly and used for fertilizer purposes even has a special name: Black Soldier Fly Frass Fertilizer (BSFFF) [43]. This natural fertilizer may cause an increase in the plant's biomass and the concentration of minerals contained in it [44]. Fertilizer obtained from insects can also be a valuable source of organic material, which is particularly important for farms that do not have animals and have not used organic fertilizers for years [45]. However, the number of articles devoted to the role of frass as fertilizers is relatively small [46]. Photosynthesis is the most important process occurring in a plant and its measurement can be a key indicator not only of the plant's health but also its adaptation to stressful conditions. Drought stress in particular has a strong impact on the photosynthesis process, because the first defense mechanism of plants against water shortage is the closure of stomata, which further leads to a chain of processes that reduce the efficiency of photosynthesis and, consequently, a decrease in yield. The nutrition supplied to plants determines their health and also affects the effectiveness of photosynthesis [47; 48]. In this work, we investigated how waste from _H. illucens_ production affects plant yield and chemical parameters, and whether its use increases the resistance of plants to drought stress. We conducted our research on lettuce plants, which are one of the most important vegetable species in the world. Lettuce belongs to the Astaraceae family and is a temperate climate plant that today also grows in other climatic conditions, both in fields and in greenhouses. It is also the most consumed vegetable in the world. The largest producer is China, which grows stem lettuce, which is not very popular in other parts of the world, such as Europe. The United States contributes 22% of production, where it ranks third in terms of consumption [49]. It is the main salad plant, usually eaten raw, which allows for better utilization of the nutrients contained in it by the body. It is used in sandwiches and salads. However, the use of lettuce can be much broader. Oil can be pressed from the seeds, and even cigarettes can be made from the leaves. Wild forms were used to produce Lacturarium, used as a sleep aid in ancient Egypt [50]. Lettuce is a plant that is widely used in agricultural research. One of the reasons for this is the short cultivation cycle and relatively easy agrotechnics. Many studies focus on improving the yield and nutritional value of this plant [51], as it is a source of nutrients but also compounds beneficial to human health. Among lettuces, leafy lettuce contains a larger amount of minerals, vitamins and bioactive compounds than crunchy lettuce. The content of folic acid is similar to that of other vegetables. Young lettuce is particularly popular [49]. The best quality of lettuce is achieved through appropriate fertilization and proper irrigation [52]. The value of lettuce in human nutrition is determined by its nutritional properties--a high content of vitamin C, polyphenols, antioxidants and fiber. Research indicates the role of lettuce in preventing many diseases. Due to these factors, lettuce is an economically important plant [53]. We expect that the use of grass in plant fertilization will lead to similar effects to typical natural fertilizers, in particular, manure. Fertilized plants should have a higher nutrient content and tolerate drought better. The results may provide evidence that insect frass is also as effective as classic natural fertilizer, or maybe even better. Fertilizers of this type may also contribute to a circular economy. Whether their use increases the resistance of plants to drought stress is investigated.