"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

January 30, 2011

Allomermis solenopsi

It seems that ants just can't get a break when it comes to parasites. When they are not being persuaded to clamp themsleves to the top of a grass blade for a nightly sacrificial ritual (Dicrocoelium dendriticum), they are doing impersonations of a juicy berry thanks to some worms in their gut (Myrmeconema neotropicum). Today's parasite adds to the insult and takes its ant host for an impromptu swim, then leaves it to drown. Allomermis solenopsi is a nematode from the Mermithidae family, a group of nematodes which have plagued insects for at least 40 million years. While they superficially resemble nematomorph hairworm (e.g. Spinochordodes tellinii) and have a similar life-cycle, these worms actually belong in a separate phylum. However, the mermithid nematodes have convergently evolved the same ability as the hairworms to manipulate their hosts - namely, taking the host for a suicidal trip to the pool. Allomermis solenopsis develops inside the gaster (abdomen) of the ant and when it reaches maturity, it needs to exit into a body of water to mate and lay eggs. Other species of mermithids are well-known for inducing water-seeking behaviour in their hosts, so given that the nematode would dry out very quickly if it becomes exposed to the outside environment, it is likely that when the time comes, A. solenopsi just takes its ant for a terminal dunk.

Image from figure of the paper.

Poinar Jr, G.O., Porter, S.D., Tang, S. and Hyman, B.C. (2007) Allomermis solenopsi n. sp. (Nematoda: Mermithidae) parasitising the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) in Argentina. Systematic Parasitology 68: 115-128.

Contributed by Tommy Leung.

January 24, 2011

Nearctopsylla brooksi

Many fleas are quite host specific, although rodent and shrew fleas are occasionally also found on their predators, probably hopping on the nearest warm body when their host is killed. Fleas of the genus Nearctopsylla are primarily found on shrews and moles, but N. brooksi has so far only been reported from weasels (Mustela spp.). It is unlikely to be a weasel parasite so the true host has yet to be discovered. The flea in the photo was found on…you guessed it…a long-tailed weasel.

Contributed by Mike Kinsella.

January 14, 2011

Arthurhumesia canadiensis

Parasites come in all kinds of bizarre shapes and you don't get much more bizarre than today's parasite - Arthurhumesia canadiensis. This species is a parasitic copepod that lives inside the intestine of the compound ascidian (sea squirt) Aplidium solidum. The diagram shows a female specimen, with a pair of lobe-like egg sacs attached. And if you are wondering "what's the weird little blob the arrow is pointing at?", well that's the male copepod. This weird little crustacean is named after Arthur Humes - a very prolific taxonomist. Over the course of 60 years, he was responsible for describing over 700 new species of parasitic copepods. So it's only right that a copepod named after him would appear on a blog which is about parasite biodiversity!

Bresciani, J. and López-González, P.J. 2001. Arthurhumesia canadiensis, new genus and species of a highly transformed parasitic copepod (Crustacea) associated with an ascidian from British Columbia. Journal of Crustacean Biology 21(1): 90-95.

Contributed by Tommy Leung.

January 10, 2011

Alaria marcianae

This horned little devil is the mesocercaria of the trematode, Alaria marcianae, which has a very unusual life cycle. When the metacercariae of this species are ingested by a lactating carnivore such as a Florida panther, they migrate to the tissues instead of developing in their normal site, the small intestine, and develop to this stage. They can then be passed in the milk to the kittens, where they develop normally in the intestine to the adult stage. Females can continue to transmit mesocercariae to future litters until exhausted of their infections.

Contributed by Mike Kinsella.

January 1, 2011

After One Year, Just the Tip of the Iceberg

Throughout this year we've met blood-feeders, mind-benders, parasitic castrators, brood usurpers, outrageous shape-shifters, skin-clingers, eye-invaders and deadly plagues, but this is only a minuscule fraction of the true biodiversity of parasites. For some perspective let's calculate the number of years it would take to feature all the known metazoan parasites (such as worms, lice, and other multicellular animals) at a rate of one per day:

Myxozoa >1350 = 3.70
Trematoda >18000 = 49.30
Monogenea >20000 = 54.95
Cestoidea >5000 = 13.67
Acanthocephala >1200 = 3.29
Nematoda >10500 = 28.77
Mollusca >5600 = 15.34
Arachnida >30800 = 84.38
Crustacea >5360 = 14.68
Insecta >9400 = 25.75

Even without the odds and ends with less speciose groups like the Nematomorpha and Pentastomida, it would take us a little over 295 years just to feature every known and described species of metazoan parasites. This number does not include the multitude of undescribed species out there; a recent study (Randhawa and Poulin 2010) estimate that 3600 species of tapeworms are yet to be described from elasmobranchs (sharks and rays) alone - so that's another 10 years worth of tapeworms, all undescribed. The number of species of monogenean yet to be described is greater still, with 21000 - 22000 species yet to be described (Whittington 1998) - that's more than another 57 years' worth. For the digeneans, parasitic flukes, in Australia alone, over 5500 species are yet to be described (Cribb 1998) - 15 years worth of worms. All undescribed and unknown to science.

And that is just from the flatworms, which form one phylum out of many. What about the arthropods? And the nematodes? There is no reasons to think why there would be any fewer undescribed parasitic arthropods and nematodes than there are undescribed parasitic flatworms, and if such trend holds, it is likely that it would take an entire millennium to feature all described and undescribed species of metazoan parasites.

But that in itself is merely the tip of a very, very large iceberg. Moving away from the animals, what about the many parasitic fungi and plants? Parasitism as a life-style is just as common in fungi and plants as they are in animals. What about the eukaryotic single-cell parasites? This include the apicomplexans and the trypanosomes, which include parasites which cause diseases like malaria and sleeping sickness.

On top of that, throughout the year, we also featured many pathogenic bacteria and virus, and their diversity readily dwarfs the diversity found in the eukaryotes. With the use of new technology such as metagenomics, we have only begun to scratch the surface of their mind-boggling diversity. For this blog, we have looked beyond the traditional definition of a "parasite" to also included phytophagous insects (which technically are merely insects that are parasitic on plants rather than animals), and animals which have some aspect of "parasitism" to their life-style, such as brood parasites and kleptoparasites.

The Year 2010 was named as the "International Year of Biodiversity" and this blog was our attempt at showing the amazing, cool, and sometimes gross diversity just in parasitic organisms. But, we have barely scratched the tip of the iceberg with this blog and if this iceberg represents all the species which have been described, then it is merely a small chunk from a much greater ice sheet. Any study of biodiversity that does not take parasites into account will be ignoring the elephant in the room...or should I say the lively colony of critters living in and on the elephant?

We hope that you have enjoyed your daily dose of parasites throughout 2010. We'll continue to add other posts on cool and new and interesting parasites, so please follow the blog if you want to be alerted when these are added.

Finally, a big thank you to the more than two dozen people who contributed over the year and a HUGE thank you to all of you for reading this, sharing this, and giving us your comments and questions.


Cribb, T. H. 1998. The diversity of the Digenea of Australian animals. International Journal for Parasitology 28: 899-911.
Randhawa, H.S. and Poulin, R. 2010. Determinants of tapeworm species richness in elasmobranch fishes: untangling environmental and phylogenetic influences. Ecography 33: 866-877.
Whittington, I.D. 1998. Diversity "down under": monogeneans in the Antipodes (Australia) wih a prediction of monogenean biodiversity worldwide. International Journal for Parasitology 28: 1481-1493.

-- By Tommy Leung and Susan Perkins