Endogenous retroviruses are abundantly embedded within host genomes and provide a unique snapshot of multiple past viral infections. They are thought to be evolutionarily related and structurally similar to LTR retrotransposons, yet retroviruses primarily differ by a canonical fusogenic Envelope protein crucial for cell-cell infectivity. We have discovered a group of active transposons in the Drosophila ovary that mimic retroviral behavior - demonstrating infectivity traits - despite the absence of an Envelope-coding gene. We further identified an alternative infectivity gene encoded in the genomes of these transposons, potentially substituting the Envelope's role in enabling cell-cell transmission. By mining genomes, we found such infectivity genes to be widespread in the context of transposons across insects. These findings, which call attention to the concepts of infectious transposons or Envelope-less retroviruses, necessitate reconsideration and redefinition of the conventional boundaries between transposons and viruses.