Horse-hair worms

Horse-hair or Gordian Worms

The return of almost daily thunderstorms from mid-January has seen the return of many insects to the light sheet. This is quite surprising because the prolonged drought would lead one to believe that populations might be reduced and take some time to return to normal.


With the orthopteroids that have made their recent appearance, it seems that there is a high percentage of individuals carrying Gordian Worms (Nematomorpha). I have found parasitised grasshoppers, katydids and cockroaches and mantids.

Horse-hair worms are so-called because of their appearance and often when encountered they appear as a Gordian Knot. When not in their insect hosts the worms are often found in puddles, streams or even horse troughs. But how do they get there?

Much more study is needed to understand the biology of Australian Nematomorpha. Poinar and Weissman (2004) present the potential life cycles for some North American species. It seems that several hosts are involved. An infected insect is "directed" towards water. There the worm emerges and the host dies. In the water the worms mate, lay eggs and the eggs are ingested by an aquatic insect which is eventually eaten by another host. The larva of the worm bores through the host's gut and resides in the body cavity where it feeds on haemolymph, testes and ovaries. This, of course, renders the host sterile. But it continues to live and may even moult with the developing worm within.

2019-20 has seen an inordinate number of parasitisms in the rainforests around Kuranda. Reasons for this are not known.

See this but not whilst eating:  https://www.youtube.com/watch?v=YB6O7jS_VBM

This adult male katydid had multiple worms within its body cavity. It is surprising that such a mass of worms could come out of a small katydid.

The darkened abdomen of the host reveals its contents-many Gordian worms.

Another katydid with the live worm emerging. One worm measured 26 cm, the other 28 cm. Both were within the katydid.

Crickets are also infected. Thi is an adult female Unka boreena Otte and Alexander  with the worm emerging.

This tiny blattelline cockroach, Beybienkoa kurandensis Roth is infected. The worm, probably a different species from the ones above, can easily be seen through the integument.

An adult male pseudophyllodromine cockroach, Balta denticauda Hebard with a Gordian Worm emerging.

Mantids, such as the Snake Mantid, Kongobatha diademata Hebard have been infected this year. The factors causing this increase in the number of Gordian Worm infections are at this point only speculative.

Thanks to George Poinar for comments on Gordian Worm parasitism.

Literature

Poinar, GO, Weissman DB. 2004. Hairworm and nematode infections in North American Jerusalem crickets, field crickets, and katydids (Orthoptera, Stenopelmatidae, Gryllidae and Tettigoniidae). Journal of Orthoptera Research 13(1): 143-147.