1. Ova .......... Go to: 3 & 4
2. Adult Worms seen in feces or on palpation glove .......... Go to: 9 & 10

3. Ova with a single operculum. (Ova also larvated and elongate oval) ........ Oxyuris equi
4. Ova without an operculum. ........ Go to: 5 & 6

5. Ova embryonated or larvated, (short oval to ellipsoid shape) ........ Strongyloides westeri
Ova NOT Embryonated or Larvated ........ Go to: 7 & 8

7. Ova round with a rough coat around the shell and a single-cell stage ........ Parascaris equorum
8. Ova ellipsoid, smooth shelled with morula stage ........ Strongyle-type ova (large strongyles, small strongyles)

9. Adult nematodes are very large, more than 3 inches (7.5 cm) long, with 3 large lips ........ Parascaris equorum
10. Adult nematodes less than 3 inches (7.5 cm) long, without 3 large lips ........ Go to: 11 & 12

11. Adult nematodes possess a long attenuated, pointed tail ........ Oxyuris equi
12. Adult nematodes do NOT possess a long attenuated, pointed tail ........ Go to: 13 & 14

13. The buccal cavity is short & square ........ Small strongyles
14. The buccal cavity is very large and round ........ Large Strongyles =(Strongylus spp.)