Do fleas have eyes?

adult cat flea eyes

Tom Murray

Img 1 Adult cat fleas have a black, round, simple “eyespots”, one on each side of the head.

Summary

Adult cat fleas do have eyes. One is located on each side of the head. Instead of compound eyes, fleas posses simple eyes with a single biconvex lens. The eyes are black and round.

Details

Location & Appearance

Fleas have two small eyes, one on either side of their heads Img 1 & 2. The eyes sit slightly beneath, and ahead of, the base of the antennae. They’re located in the same position where most insects have compound eyes.

flea eyes are black

Chris Hedstrom

Img 2 Magnified image of a cat flea, clearing showing its eye spot.

Flea eyes are round with a black pigment. They appear as dark spots on the head. The eyes closely resemble the dorsal ocelli of other insects Img 3.

The Structure of Simple Eyes

Fleas don’t have compound eyes. Instead, they posses simple eyes with a single biconvex lens. Long sense cells reach from the base of the eye to the lens, but they don’t form rhabdoms. There are a few small corneagenous cells. The entire inner eye is surrounded by a black pigmented sheath.

adult cat flea eyes resemble ocelli

USGS Bee Inventory and Monitoring Lab

Img 3 Fleas have simple eyes that resemble the dorsal ocelli (highlighted) of other insects.

The eyes of fleas are sensitive to changes in light intensity, but they can’t form visual images. Still, visual cues play a major role in host-finding.

Flea Eye Evolution

It’s been theorized that fleas eyes were once dorsal ocelli, and they got displaced from the top of their heads to the sides. However, it’s now believed that they’re actually reduced and modified compound eyes. Through the course of evolution, the compound eyes were replaced with heavily sclerotized, ocelli-like “eyespots”.

References

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