Did you know: male swallowtail butterfly has eyes on it's 'penis'?

some male swallowtail butterflies have light-sensitive cells, essentially "eyes," on their genitalia. These cells, located on the scaphium and ovipositor, help males position themselves correctly during mating. The photoreceptors detect changes in light, particularly when the male is properly aligned with the female, triggering the mating process.
Here's a more detailed explanation:
Discovery:
The presence of genital photoreceptors in butterflies was discovered in Japanese yellow swallowtail butterflies.
Location:
These photoreceptors are found in both male and female butterflies, with males having them on the scaphium and ovipositor.
Function in Males:
In males, the photoreceptors help guide them to the correct position for copulation by detecting light changes as they align with the female's genitalia.
Function in Females:
In females, the photoreceptors are thought to help with proper ovipositor positioning during egg-laying.
Importance:
The photoreceptors are crucial for successful mating. In experiments, males without functional photoreceptors had significantly lower mating success rates.
How they work:
The photoreceptors are covered by transparent cuticle and are sensitive to light. When light is detected, it signals the butterfly to continue aligning for mating. When the light is blocked (as when correctly aligned), the signal stops, indicating the correct position.
Not Limited to Swallowtails:
While discovered in swallowtails, these genital photoreceptors are found in all butterflies and skippers, but not in moths.