Jun 072012
 

UPDATE: It turns out my first theory involving oestrid bot flies was full of holes. I’ll leave it up because the biology of the individual parasites is accurate and interesting, but see the bottom of  the post for an accurate description of what happened in the photo. I apologize for the misinformation.

Recently, I was catching up on Twitter late at night when @PsiWaveFunction shared a link to a photo on Reddit that stopped me cold in my tracks and that has kept me morbidly fascinated since. I’ve spent the better part of a day thinking about the photo, and I think I’ve pieced together the series of events and organisms that lead to the case of the mystery myiasis. If my theory is correct, this might be one of the coolest cases of parasitism I’ve ever encountered, and features a fly who’s life history beautifully illustrates the intricacies of evolution, another fly that’s threatening the birds which helped Darwin develop his theory of evolution through natural selection, and a bird who is being selected against by the worst possible luck.

Normally I’d include the photo in question right about here, but out of respect for those victims readers who are a tad squeamish at the sight of parasites (or birds), I’ll simply link to it and allow your curiosity to battle your better judgement1. I’ll give you a moment to decide and, should you accept the challenge, digest what you’ve just seen.

“This baby bird has no face… only maggots”

So, were you amazed? Disgusted? Wondering what the hell you were looking at? If you’re like me, you probably felt a little bit of all three, and then immediately went back to take a closer look.

Welcome to the wonderful world of warble flies (family Oestridae)! Each of those oddly formed lumps is actually a bot fly maggot which has burrowed beneath the skin of the chick to feed and develop. You’ll notice two dark marks on the exposed end of each maggot; these are the spiracles through which the maggot breathes. After a few weeks, each of the maggots will wriggle free from the bird, drop to the ground and pupate, eventually emerging as an adult ready to breed. Normally the host is left mostly unharmed after providing safe harbour for a bot fly, but in this case I suspect the bird might have problems due to the shear number of maggots present (at least 15 that I could make out).

Dermatobia hominis

Dermatobia hominis -- Photo by J. Eibl, Systematic Entomology Laboratory, USDA.

What’s odd about this situation2 is that these bot flies have parasitized a bird. You see, almost all bot flies are mammal parasites, infesting anything from rodents to elephants, and are usually very specific about their host species. One bot fly however, Dermatobia hominis, is a generalist, and has been recorded infesting a number of different animals, from humans and monkeys to dogs and cats, and of relevance to this story, birds on occasion. In a family of narrow specialists, it’s a wonder that D. hominis is such a broad generalist; until you learn how D. hominis distributes its offspring — by hijacking other flies to serve as expedited egg couriers.

Psorophora sp. (Culicidae) with D. hominis eggs attached.

Psorophora sp. (Culicidae) with D. hominis eggs attached. Illustration by A. Cushman, Systematic Entomology Laboratory, USDA.

After mating, female D. hominis will snatch up other parasitic flies, like mosquitoes, flesh flies and muscid flies3, and lay a clutch of eggs on the enlisted fly. When the carrier fly locates and lands on a host to feed4, the body heat of the victim signals the bot fly egg to hatch and fall from the carrier onto its new home, where it quickly burrows in to begin feeding. This amazing life cycle means that the female bot fly has little control over where, and on what species, its offspring ultimately end up infesting, resulting in a nearly random generalist parasite that must be able to survive on whatever host it finds itself on, including our small bird.

Obviously the natural world is a complex system, and unfortunately for our bird, it’s full of a diverse array of parasites, all looking for a free meal. Let me introduce you to another player in this saga, Philornis downsi (Muscidae), a fly native to continental South America and Trinidad & Tobago, where our unfortunate bird lives.

Philornis in bird beak O'Connor et al. 2010

Philornis in nasal cavity of deceased bird. Image from O'Connor et al. 2010

While adults are unassuming, feeding on pollen and nectar, Philornis downsi larvae are brood parasites of nesting birds. Hiding out of sight during the day in the bottom of the nest, maggots emerge after dark to crawl within the nasal passages of developing chicks, feeding on their blood and tissue, sapping their energy. As the maggots continue to grow, they begin feeding elsewhere on the nestlings, causing severe damage and ultimately death. Throughout the Galapagos, where the fly was introduced sometime prior to 1964, Philornis downsi has been causing nestling mortality rates as high as 95% in Darwin’s finches, the unique birds who’s diverse beak shapes inspired Charles Darwin’s theory of evolution by natural selection. While there has been a great deal of work done on P. downsi in the Galapagos in an effort to save these ecologically important birds5, I assume it is also receiving research attention in its native range, which is where we return to Reddit, our original photo and what I think happened.

Of all the parasites, in all the nest boxes, in all the world, she flies into mine.

The photo that began all this was uploaded to Reddit by marrgalo, who explained they found the bird while monitoring bird nests on Tobago for Philornis downsi as part of their research program. Tobago is also well within the range of Dermatobia hominis. Here’s what I think may have happened:

My theory was wrong. See below for information about the actual parasite.

  • A recently mated female Dermatobia bot fly was looking for a carrier fly
  • A female Philornis downsi happened to fly by, was quickly snatched by the bot fly and entrusted with a load of bot fly eggs
  • The female Philornis was released, and continued her search for a bird’s nest to deposit her eggs in
  • Finding a nest, the Philornis female walked around, laying eggs among the nesting material, and happened to tread across the young bird in the nest

  • The bot eggs, sensing the proximity of a warm-bodied host, hatched and quickly found their way to the unlucky bird’s face
  • The Philornis female finished laying her eggs and took off from the nest, leaving chaos brewing in her wake
  • Later, a social media-conscious research assistant comes along, finds the disfigured nestling, and does the only logical thing; takes a picture and posts it to the internet for all to enjoy!

Of course, this is only a theory based on a single photo and a very small fraction of information about the team’s research, but given the evidence and biology of the species potentially involved, I think it’s certainly a plausible hypothesis. There are a lot of potential fallacies in my theory, like whether the bot fly larvae are actually Dermatobia, or whether Dermatobia even uses Philornis as a vector (although it’s known to use 11 species of Muscidae), but these are the sort of questions that can be observed and tested eventually. Hopefully the researchers behind the photo will rear the maggots from the bird’s face, identify the parasites involved, and then publish their work so I can find out whether any of these ideas turned out to be accurate6.

Whether my theories were correct or not, the fact that they’re even plausible keeps me interested and excited about entomology and the intricate roles parasites play in our daily lives!

References:

ResearchBlogging.org

Eibel, J.M., Woodley, N.E. 2004. Dermatobia hominis (Linnaeus Jr., 1781) (Diptera: Oestridae). The Diptera Site. Accessed June 6, 2012. http://1.usa.gov/MbTexi

Fessl B, Sinclair BJ, & Kleindorfer S (2006). The life-cycle of Philornis downsi (Diptera: Muscidae) parasitizing Darwin’s finches and its impacts on nestling survival. Parasitology, 133 (Pt 6), 739-47 PMID: 16899139

O’Connor, J.A., Robertson, J. & Kleindorfer, S. (2010). Video analysis of host–parasite interactions in nests of Darwin’s finches, Oryx, 44 (04) 594. DOI: 10.1017/S0030605310000086

 

UPDATE June 7, 2012 @ 3:30PM EST: It turns out that the maggots in the bird’s face aren’t Dermatobia hominis, or even bot flies of the family Oestridae at all! After doing some further research, I’ve learned that they are more likely to be another species of Philornis fly. I was totally unaware that there were flies outside of the oestrid bot flies which burrow into the skin of hosts and form warbles like these, but it turns out there are.

While Philornis downsi are ectoparasites that feed on nestling birds as I described, it seems that there are several species in the same genus which burrow within the skin and form welts similar to oestrid bot flies. Here’s an example of Philornis vulgaris infesting a Tropical Mockingbird nestling from Colombia:

Philornis vulgaris infestation Amat et al. 2007

Philornis vulgaris infestation from Amat et al. 2007

Looks vaguely familiar no? I think it’s safe to say now that this is what happened in the original photo and not the complex tale of 2 parasites like I described above.

I’m incredibly embarrassed by my Taxonomy Fail here (which holds a TFI of 11.3). Although the biology of the two parasitic species I originally discussed are accurate, the chances of them having anything to do with one another appear to be unlikely. I sincerely apologize for publishing a story that spread such inaccurate information, and I’ll do my best to not let it happen again.

Note to self: don’t assume you know anything, especially when it involves parasites.

On the bright side, I learned something new about Diptera (and humility) today, and we can all rest comfortably knowing that there are multiple, unrelated groups of flies that get under the skin of their hosts. Because I’m sure that makes everyone feel better.

 

More information about subcutaneous Philornis:

Amat, E., J. Olano, F. Forero & C. Botero 2007. Notas sobre Philornis vulgaris (Couri, 1984) (Diptera: Muscidae) en nidos del sinsonte tropical Mimus gilvus (Viellot, 1808) en los Andes de Co- lombia. Acta Zoológica Mexicana, 23(2): 205-207. http://bit.ly/LwsHh1

Uhazy, L.S., Arendt, W.J. 1987. Pathogenesis associated with philornid myiasis (Diptera: Muscidae) on nestling pearly-eyed thrashers (Aves: Mimidae) in the Luquillo Rain Forest, Puerto Rico. Journal of Wildlife Diseases 22 (2): 224-237. http://bit.ly/KlXBGR

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1- If you can’t decide, I vote you click and look. You can thank me later.

2- Beyond the whole face-of-a-million-maggots of course.

3- Among other groups including blow flies and even ticks.

4- Something these blood-sucking flies have evolved to do quite well obviously. The fact that bot flies “cheat the system” in this regard, getting their eggs to their host without needing to invest energy in complex host-finding senses, just goes to show that nothing is more awesome than evolution in action.

5- See O’Connor et al. 2010 for a good synopsis of work and observations, and check out some of the videos she’s posted to YouTube of the maggots interacting with nestlings.

6- If you happen to have research contacts in Tobago who might know about work being done on Philornis, can you let them know I’m curious? Thanks.

Dec 152011
 

Have you ever traveled to a new city and wondered where you can grab a burger, or perhaps a beer? How about wondering if there’s a good spot to bird watch or even collect a few flies in between meetings or family functions? One of the benefits of being a biologist is traveling to new locations, either to gather new data/specimens or to talk about your work on said data/specimens. Unless you have a local source of information, be it a friend, colleague or naturalist’s forum that can point you to a good park, the amount of time you spend looking for a site may equal (or be greater than) the amount of time you actually spend in the site. Wouldn’t it be great if there was a social network that could help you find natural areas faster, and let you see ahead of time what local naturalists were finding where?

foursquare logoGood news; there IS a social network capable of all these things, it’s just that no one has begun to use it for that yet! Let me introduce you to foursquare, and explain how I think it can enhance interactions between naturalists and scientists.

foursquare is a geography-based social network, allowing you to “Check in” to locations such as restaurants, events or shops and see where nearby friends have been recently. You can also leave “Tips” on things to do at a location or what’s good on the menu, and construct to-do lists of places you’d like to visit and things you’d like to do. While check-ins are only shared with your friends, the locations and tips are public and searchable, allowing you to plan trips or discover new venues.

While the network was designed for finding restaurants and bars in big cities, you can also create venues for all types of natural habitats; city greenspaces, provincial, state, or national parks (and even areas within those parks, like specific camp grounds or trails), your local arboretum, lake, or river, etc. Combine that with the Tips function and you have a GPS-enabled network which allows you to record recent nature sightings, notes on the type and quality of habitats, or anything else which may help others get the most out of their visit. Available through your web browser or on smartphones, it’s a very simple way to keep track of what you find and where!

Unfortunately I haven’t had much time in the past few weeks to explore local parks to provide you some examples, but here is the page I made for the University of Guelph Insect Collection (did I mention foursquare is a great way to increase the exposure of your local museum or natural history collection?):

University of Guelph Insect Collection on foursquare

As you can see, I’ve left a tip with some information about our collection and encouraging people to stop in and see what we do, but this is where you can leave sightings or other observations you’ve made at a location. These tips are searchable (try searching “1863 near Guelph, On” in foursquare for example), allowing people to discover potential natural history information (imagine a tip reading “Saw a bald eagle and 3 cedar waxwings today! #nature” or “Check the pond at the northwest corner for excellent dragonfly collecting #nature”). You could even go so far as to create a public list of natural areas in your region, making it even easier for others to discover new areas to explore.

So how can foursquare help naturalists and the public connect with researchers? Obviously the more people who join and record their naturalist outings in this way, the more data and locations visiting scientists may have to play with. eBird is a similar technology (without the mobile app) where birders around the world record the birds they saw, along with when and where, and which has created a near real-time database of bird diversity, ranges and migrations that is being used by ornithologists. I think by using foursquare in a similar way, researchers studying other groups can potentially do the same. Entomologically speaking, imagine the possibilities: citizen science programs tracking monarch butterfly populations, urban insect sightings (bed bugs in hotels, roaches in restaurants, etc), or taxonomists like myself finding new localities to collect in or records of uncommon species! More importantly though, is the ways in which a researcher can give back to the naturalist community. If you visit a location frequented by a local naturalist, why not meet up with them if they’re in the area, and of course share your own favourite locations and sightings for everyone to experience! I suspect that there are ways to harvest data or create secondary applications which work in concert with foursquare, but I don’t have the programming skills to explore those avenues (if you do and are interested, let me know).

Obviously for this idea to really work it will need to be adopted by naturalist communities across North America and beyond, but I think it has a lot of potential, and I’d encourage you to give it a try (and spread the word)! I’ll be continuing to record my visits and sightings, and I’ll be sure to provide future updates on how this idea progresses!

At a time when few people seem interested in the natural world around them, social media like foursquare create opportunities for us to share nature with everyone. If even one person who wouldn’t normally take the time to venture through a city park or visit an entomological museum does so because they learned of it through foursquare, I’d consider that a success!