The present investigation used Galleria mellonella larvae as an infection model to describe the virulence of Escherichia coli, the most frequent causes of several common bacterial infections in humans and animals. Some hemolymph physical properties such as hemolymph volume - and its relation to body water content, hemolymph density, and pH, along with a quantitative estimation of hemolymph proteins, lipids and carbohydrates were recorded in G. mellonella larvae at different time intervals post-injection with a sub-lethal dose (LD₂₀) of E. coli into the larval hemocoel.A decrease in fresh body weight and body water content with an increase in the hemolymph volume was observed at all time intervals post-larval treatment. This may be due to the loss of tissue water and gained it into the hemolymph. At the same time, bacterial injection decreased the hemolymph density and pH immediately following injection, while the viscosity and acidity of the hemolymph restored its original level with time. The bacterial injection also recorded an obvious decrease in the hemolymph proteins and lipids of the treated larvae at all time intervals post-treatment. This may be due to their elimination and/or their involvement in immune defence reactions or may be due to the intensive consumption and depletion of nutrition during infection. On the contrary, the levels of hemolymph carbohydrates increased at all-time intervals post bacterial injection into larvae. This increase may be due to the release of stored sugars (treehouse) which is responded strikingly due to bacterial infection causing an increase in the level of glucose and glycogen in the hemolymph. These results may lead to a better understanding of the regulatory events and the physiology of infected insects.