{"id":2194,"date":"2012-06-07T05:45:09","date_gmt":"2012-06-07T09:45:09","guid":{"rendered":"http:\/\/www.biodiversityinfocus.com\/blog\/?p=2194"},"modified":"2012-06-07T16:20:37","modified_gmt":"2012-06-07T20:20:37","slug":"a-myiasis-mystery","status":"publish","type":"post","link":"http:\/\/www.biodiversityinfocus.com\/blog\/2012\/06\/07\/a-myiasis-mystery\/","title":{"rendered":"A Myiasis Mystery – UPDATED"},"content":{"rendered":"\n

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 \u00a0the post for an accurate description of what happened in the photo. I apologize for the misinformation.<\/strong><\/p>\n

Recently, I was catching up on Twitter late at night when @PsiWaveFunction<\/a> 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.<\/p>\n

Normally I’d include the photo in question right about here, but out of respect for those\u00a0victims<\/del>\u00a0readers who are a tad squeamish at the sight of parasites (or birds), I’ll simply link to it and allow your\u00a0curiosity\u00a0to battle your better judgement1<\/sup>. I’ll give you a moment to decide and, should you accept the challenge, digest what you’ve just seen.<\/p>\n

“This baby bird has no face… only maggots”<\/a><\/p>\n

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.<\/p>\n

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).<\/p>\n

\"Dermatobia<\/a>

Dermatobia hominis -- Photo by J. Eibl, Systematic Entomology Laboratory, USDA.<\/p><\/div>\n

What’s odd about this situation2<\/sup>\u00a0is 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<\/a><\/em>, 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\u00a0D. hominis<\/em>\u00a0is such a broad generalist; until you learn how\u00a0D. hominis<\/em>\u00a0distributes its offspring — by hijacking other flies to serve as expedited egg couriers.<\/p>\n

\"Psorophora<\/a>

Psorophora sp. (Culicidae) with D. hominis eggs attached. Illustration by A. Cushman, Systematic Entomology Laboratory, USDA.<\/p><\/div>\n

After mating, female D. hominis<\/em>\u00a0will snatch up other parasitic flies, like mosquitoes, flesh flies and muscid flies3<\/sup>, and lay a clutch of eggs on the enlisted fly. When the carrier fly locates and lands on a host to feed4<\/sup>, 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.<\/p>\n

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 <\/em>(Muscidae), a fly native to continental South America and Trinidad & Tobago, where our unfortunate bird lives.<\/p>\n

\"Philornis<\/a>

Philornis in nasal cavity of deceased bird. Image from O'Connor et al. 2010<\/p><\/div>\n

While adults are unassuming, feeding on pollen and nectar,\u00a0Philornis downsi<\/em>\u00a0larvae 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<\/em>\u00a0has 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\u00a0P. downsi<\/em>\u00a0in the Galapagos in an effort to save these ecologically important birds5<\/sup>, 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.<\/p>\n

Of all the parasites, in all the nest boxes, in all the world, she flies into mine.<\/strong><\/p>\n

The photo that began all this was uploaded to Reddit by marrgalo, who explained they found the bird while monitoring bird nests on Tobago\u00a0for\u00a0Philornis downsi<\/em>\u00a0as part of their research program<\/a>. Tobago is also well within the range of Dermatobia hominis<\/em>. Here’s what I think may have happened:<\/del><\/p>\n

My theory was wrong. See below for information about the actual parasite.<\/strong><\/p>\n