1. Adult nematodes found in the Lungs of horses ........ Dictyocaulus arnfeldi
2. Adult nematodes NOT found in the Lungs of horses ........ Go to: 3 & 4

3. Adult nematodes found in the Stomach of horses ........ Go to: 5 & 6
4. Adult nematodes NOT found in the Stomach of horses ........ Go to: 7 & 8

5. Adult nematodes live in a stomach nodule and possess a Y-shaped buccal cavity ........ Draschia megastoma
6. Adult nematodes live on the stomach lining and possess a very small, indistinct buccal cavity ........ Trichostrongylus axei

7. Adult nematodes found in the Small Intestine of horses ........ Go to: 9 & 10
8. Adult nematodes found in the Cecum and Large Intestine of horses ........ Go to: 11 & 12

9. Adult nematodes are very small, less than 0.5 inches (1.0 cm) long ........ Strongyloides westeri
10. Adult nematodes are very large, more than 3 inches (7.5 cm) long ........ Parascaris equorum

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 or Strongylus spp. Go to: 15,16 & 17

15. The base of the buccal cavity lacks teeth ........ Strongylus edentatus
16. The base of the buccal cavity is armed with 2 rounded (ear-shaped) teeth ........ Strongylus vulgaris
17. The base of the buccal cavity is armed with 3 pointed teeth ........ Strongylus equinus