# Chordodes Formosanus (DD-596)

> Chordodes formosanus is a horsehair worm (phylum Nematomorpha) first described in 2011 by Ming-Chung Chiu and colleagues from specimens taken from Hierodula mantises in Taiwan and Japan. Later surveys found it in other mantises and in long-horned grasshoppers too. Horsehair worms live as adults in water. Females lay strings of eggs there, and the larvae infect aquatic insect larvae and form cysts inside them. When those insects grow up and fly to land, a mantis or cricket that eats one picks up the cyst. The worm then grows inside the host's body cavity until it fills much of the abdomen. When it's mature, the infected host heads for water, and the worm emerges and swims off to mate. Researchers have long linked this water-seeking behavior to the parasite, but exactly how it works is still being studied. A 2023 Current Biology study of the related species Chordodes fukuii found more than 1,400 worm genes that closely match mantis genes, evidence of horizontal gene transfer. Many of those genes became more active during manipulation, which suggests they may help the worm influence its host. Adult horsehair worms of different species range from a few centimeters to over 2 m long, though most are 20 to 40 cm. The specimens measured in the 2011 description of C. formosanus were about 7 to 28 cm. The footage shows a green mantis held over and then in a glass of water as a long dark worm emerges from its abdomen.

- Department: Nature (also Science)
- First published: 2025-06-14
- Last updated: 2025-06-14
- Permalink: https://detailenjoyer.com/case/chordodes-formosanus/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-596-F01**: Chordodes formosanus was described in 2011. _(Write-up · Exhibit A (A species from 2011))_
- **DD-596-F02**: A related worm carries many mantis-derived genes. _(Write-up · Exhibit D (Borrowed genes))_

## Write-up

Worms that steer mantises to water. Chordodes formosanus grows inside mantises in Taiwan and Japan.

1. **A species from 2011**: Chordodes formosanus was described in 2011 from Hierodula mantises in Taiwan and Japan.
2. **More hosts**: Later surveys in Taiwan also found it in other mantises and in long-horned grasshoppers.
3. **A two-world life cycle**: Larvae form cysts in aquatic insects, and a mantis that eats one becomes infected.
4. **Borrowed genes**: A 2023 study of the related Chordodes fukuii found over 1,400 worm genes that closely match mantis genes.
5. **How long they get**: Most horsehair worms are 20 to 40 cm, and the measured C. formosanus specimens were about 7 to 28 cm.

## Related case files

- [Hair Barrier (DD-648)](https://detailenjoyer.com/case/hair-barrier/): Another case about parasites and their hosts
- [Elytra Lift (DD-737)](https://detailenjoyer.com/case/elytra-lift/): Another close look at an insect
- [Totally Radula! (DD-292)](https://detailenjoyer.com/case/totally-radula/): I paired it with another strange invertebrate

## Reel vs. record

- **Note**: 'Reaching up to 90 cm': the specimens measured in the 2011 species description were about 7 to 28 cm. Some other horsehair worm species exceed 2 m, but most are 20 to 40 cm.
- **Note**: 'Secretes proteins to exit the host': I found no source for this. The mature worm leaves through the host's body wall when the host is in or near water.
- **Note**: 'Manipulate the mantis' nervous system': infected hosts do seek water, but the mechanism isn't fully understood. A 2023 study of the related Chordodes fukuii found mantis-derived genes that may play a role.
- **Note**: 'After the mantis consumes an infected insect': yes. Larvae form cysts in aquatic insects, which carry them to land when they become adults.
- **Missing**: the species was described in 2011 from Hierodula mantises in Taiwan and Japan, and later found in other mantises and long-horned grasshoppers.

## Video: Chordodes Formosanus: Worms That Steer Mantises to Water

- Duration: 24.3 s · Published: 2025-06-14
- File: https://detailenjoyer.com/assets/videos/DK4ur3rRdDY.mp4

### Transcript

DID YOU KNOW? Submerging a praying mantis in water can reveal a grim parasitic phenomenon. Horsehair worms, specifically Chordodes formosanus, infect the mantis by growing inside its abdomen after the mantis consumes an infected insect. These worms, reaching up to 90 cm, manipulate the mantis' nervous system, compelling it to seek water. When submerged, the mature worm secretes proteins to exit the host, wriggling out as a long, threadlike form. NOW YOU KNOW!

## Questions & answers

**Q: When was Chordodes formosanus described?**  
A: From Hierodula mantises in Taiwan and Japan. _(Source: Write-up · Exhibit A (A species from 2011) · Chiu et al. (2011): A new horsehair worm, Chordodes formosanus sp. n., from Hierodula mantids of Taiwan and Japan, ZooKeys (PMC))_

**Q: Which mantis genus is its main host?**  
A: Hierodula mantises. _(Source: Write-up · Exhibit A (A species from 2011) · Chiu et al. (2011): A new horsehair worm, Chordodes formosanus sp. n., from Hierodula mantids of Taiwan and Japan, ZooKeys (PMC))_

**Q: How does a mantis get infected?**  
A: Cysts form in aquatic insects. _(Source: Write-up · Exhibit C (A two-world life cycle) · Hanelt: Introduction to the Nematomorphs, Concepts in Animal Parasitology; UC IPM: Horsehair worms)_

**Q: How many mantis-like genes did the 2023 study find in C. fukuii?**  
A: Evidence of horizontal gene transfer. _(Source: Write-up · Exhibit D (Borrowed genes) · Mishina et al. (2023): Massive horizontal gene transfer and the evolution of nematomorph-driven behavioral manipulation of mantids, Current Biology)_

**Q: How long were the measured C. formosanus specimens?**  
A: From the 2011 species description. _(Source: Write-up · Exhibit E (How long they get) · Chiu et al. (2011): A new horsehair worm, Chordodes formosanus sp. n., from Hierodula mantids of Taiwan and Japan, ZooKeys (PMC); Hanelt: Introduction to the Nematomorphs, Concepts in Animal Parasitology)_

## Sources

- [Chiu et al. (2011): A new horsehair worm, Chordodes formosanus sp. n., from Hierodula mantids of Taiwan and Japan, ZooKeys (PMC)](https://ncbi.nlm.nih.gov/pmc/articles/PMC3253628/)
- [Chiu et al. (2017): A new orthopteran-parasitizing horsehair worm, Acutogordius taiwanensis, with a redescription of Chordodes formosanus and novel host records from Taiwan (PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC5523353/)
- [Mishina et al. (2023): Massive horizontal gene transfer and the evolution of nematomorph-driven behavioral manipulation of mantids, Current Biology](https://doi.org/10.1016/j.cub.2023.09.052)
- [Hanelt: Introduction to the Nematomorphs, Concepts in Animal Parasitology](https://wisconsin.pressbooks.pub/animalparasitology/chapter/ben-hanelt/)
- [UC IPM: Horsehair worms](https://ipm.ucanr.edu/home-and-landscape/horsehair-worms/)

## Cite this case file

Easterling, Marcus. "Chordodes Formosanus." The Detail Department (DetailEnjoyer), case file DD-596, last updated Jun 14, 2025. https://detailenjoyer.com/case/chordodes-formosanus/