Abstract Scanning electron microscopy (SEM) allowed observing Beauveria bassiana and Metarhizium anisopliae adhesion and penetration structure on Agrotis ipsilon larvae. SEM of A. ipsilon larvae treated with the Lc50 of the fungus, B. bassiana revealed adhesion and penetration structures in the infected larvae. Growth of the fungus on the infected larvae and signs of hyphal penetration of insect cuticle as well as proliferation of the cuticle were also appearing. On the other hand, the fungus, M. anisopliae as declared by SEM showed a dense network together and cause the green spores on the insect cuticle. Also, SEM allowed observing the spores and hyphae of the fungus in the body cavity of infected larvae. Scanning electron microscopy is allowed tool to observe the mode of action of entomopathogenic fungi and to observe how they are able to colonize and infect the host.