Adult fleas are very small, typically measuring about 1/8 of an inch long, which is approximately 1 to 3 millimeters in length

. The size can vary slightly depending on the species and sex; for example, female cat fleas average around 2.5 mm, while males can be less than 1 mm long

. Fleas are wingless, flat, and dark reddish-brown in color, with bodies adapted for moving quickly through the fur of their hosts

. In summary:

• Typical adult flea length: 1 to 3 mm (about 1/8 inch)
• Female fleas are generally larger than males
• Fleas are small enough to be difficult to spot but visible to the naked eye
• Size comparable to a poppy seed or smaller than a black peppercorn

This size allows fleas to easily move through the hair or fur of animals and makes them challenging to detect without close inspection