Ascaris lumbricoides


Virtual Microscope

Ascaris lumbricoides egg

In the stool of the infected host, two types of Ascaris lumbricoides eggs can be found: fertilized and unfertilized.

Fertilized eggs have a rounded shape and feature a thick shell with an external mammillated layer, which is often stained brown by bile. In some instances, the outer layer may be absent, resulting in what is known as decorticated eggs. These fertile eggs typically measure between 45 to 75 µm in length and 35 to 50 µm in the width.

On the other hand, unfertilized eggs are elongated and larger than their fertile counterparts, reaching lengths of 80 up to 90 µm and 40 to 45 µm in the width. Their shell is thinner, and the mammillated layer shows greater variability, with either prominent protuberances or almost none. Unfertile eggs primarily consist of a mass of refractile granules.

A Shell
B Embryo

Typical mouth of Ascaris spp.

Both male and female adults have three distinct "lips" located at the anterior end of their bodies.

Adults of A. lumbriucoides


  • large roundworms


  • typically longer
  • measuring 20–35 cm
  • Straight tails


  • smaller
  • Ranging from 15–31 cm
  • Curved tails