More Urban Species: Rabbit/Rodent Botfly

[urbpan]

Rabbit/Rodent Botfly
Cuterebra sp.

If you would like to have a pleasant lunch out, do your best to avoid being seated by any group composed mostly of women wearing scrubs.  In all likelihood, they are veterinarians and vet techs, and you don't want to overhear their conversation while you are eating.  One of these professionals and I were discussing what disgusting things we had witnesses--she worked in ophthamology, which in my book, means she automatically wins this particular discussion.  She admitted that one thing she can not abide, is Cuterebra.  She said the word like it was just another disorder, like "hernia" or "Chlamydia."  In fact Cuterebra is the genus of an animal sometimes encountered in the animal medicine world: the botfly.

Adult botflies are striking creatures, and some Cuterebra botflies are downright beautiful, with bee-like markings and huge eyes with red spots on them.  Their eggs are deposited in places where rodents or rabbits will pass by, such as the edges of burrows.  In response to the body heat of a passing mammal, the egg hatches and the tiny larva is brushed onto the mammal's fur or skin.  The larva makes its way to an opening--the nose or mouth, or perhaps a small injury, and goes inside.  Different Cuterebra species then find their way to different locations under the skin, and encyst themselves.

They grow fat on the flesh of their host, reaching up to 4 centimeters in length by the time they are ready to pupate.  The pupa drops from the host animal and remains in the soil or leaf litter until it metamorphoses into an adult fly.  This stage varies by temperature; in colder times it may take six months or more.  The adult has vestigial mouth parts and eats nothing at all, surviving for a matter of days simply to mate and reproduce.

This bot's host, a rat (Rattus norvegicus), died prematurely.
The bot didn't stay encysted,opting instead to emerge.

The botfly's life cycle is not entirely unlike that of the oak apple gall wasp.  Instead of protection in a gall made from the tissues of a plant, the larva hides in lump of flesh that goes by the old fashioned sounding term "warbles."  A small pore in the lump allows the maggot to breathe.  While the larva is encysted it secretes antibiotic and analgesic chemicals--it would be a problem if the host experienced enough pain to try to dislodge its passenger, and living in an open wound requires keeping the bacteria at bay.  After dropping out, the bot has no more need to pamper its former home in flesh, and infections may develop.  Wild populations of rodents and rabbits may rise and fall in response to the weakening effect of botfly parasitism.

Cuterebra maggots do their best to get into a rabbit or a rodent, but sometimes they climb on board some other mammal.  The fact that vets and vet techs are on a first name basis with the fly indicates that cats and dogs (and ferrets) are sometimes subject to warbles.  Treatment is careful surgical removal--damaging the bot invites infection.  Alert readers, and those prone to hypochondria will be aware that humans are also mammals.  Cuterebra infection in humans is blissfully rare, probably because our species spends relatively little time in rodent burrows. 

In the tropics humans can be occupied by Dermatobia hominis, a botfly whose taste in hosts is revealed by its scientific name.  This clever fly essentially mugs a mosquito and glues its eggs to the bloodsucker's back.  When the mosquito bites a human (or other primate--this animal evolved in South America alongside monkeys rather than us apes) the eggs hatch and the maggots start their subcutaneous adventure, more or less as described above.

Other botflies are specially adapted to parasitize different mammals.   There are botflies in the Old World for horses, sheep, and camels, but Cuterebra is the only genus native to North America.  There are thirty or so species described, but scientists admit to gaps in their knowledge, despite active interest and study of this group.


The unencysted bot is doomed.

Sources and further reading:
 
The Merck Veterinary Manual.  Cuterebra Infestation in Small Animals: Introduction

Florida Entomology:   CUTEREBRA BOT FLIES (DIPTERA: OESTRIDAE) AND THEIR INDIGENOUS HOSTS AND POTENTIAL HOSTS IN FLORIDA

Michigan Department of Natural Resources: Warbles.

Journal of Clinical Microbiology.  Tracheopulmonary Myiasis Caused by a Mature Third-Instar Cuterebra Larva: Case Report and Review
(This is a particularly unusual case of human infestation.)

Dave's Garden.  Images of the bug Rabbit Bot Fly (Cuterebra buccata)
A gorgeous photo of an adult fly.

There's an abundance of scientific articles about this subject.  I didn't even bring up the tree squirrel botfly Cuterebra emasculator.  Any guesses as to what part of the squirrel's body the bot lives in?

Comments

[badnoodles.livejournal.com]

I love bot flies so very, very much.

[txtriffidranch.livejournal.com]

I understand. All that little bot needs is Ian Holm standing over it, screaming "Don't touch it! Don't touch it!" at Yaphet Kotto.

[urbpan.livejournal.com]

I have two questions for you related to botflies and dead hosts: First, where did the bot I photographed above think it was going? (In other words where will a bot go to escape a sinking rat?)

The second question is below, from giggling wizard.

[badnoodles.livejournal.com]

Most likely, it was going to try to pupate, even though it wasn't quite fully developed. This happens in a lot of Cyclorraphan fly species if you prematurely remove them from a food resource.

Their odds of survival aren't good, since they lack the full nutrient quota they need to survive the pupa sate. And even if they make it, they'll be small, less-fit adults. But they have a better chance than if they remain in the rat, which will decompose rapidly or be be consumed by carrion-eaters.

[ssorca19.livejournal.com]

<~ has often been one of the women at that table.

Its also fun to bring this up at the dinner table surrounded by your squeamish family ;)

[txtriffidranch.livejournal.com]

At times, I envy you. In my case, I try to have a good rational discussion about parasites at dinner, and these always end with my wife burying her incredibly sharp elbows into my skull, screaming "What the hell is WRONG with you, HUH?" (All I did was answer her question about the only good thing about cockroaches on old-time sailing ships: "How else are you supposed to keep the lice under control?" Thanks to my picturing what would have happened if we'd had kids, with our firstborn regaling a first-grade class with the science fair project "How does Brundlefly eat?", I now have a dent in the top of my skull that I can use as a candleholder.)

[ssorca19.livejournal.com]

hahaaha luckily my wussy family does not tend toward violence lol.

[txtriffidranch.livejournal.com]

In some ways, that's a shame. My father's side of the family comes from good Brit/Scot Catholic stock, where the filthiest four-letter words you can utter in public are "Last call." Our family reunions tend to resemble the last fifteen minutes of a George Romero film.

[urbpan.livejournal.com]

To be fair, once someone asks a question about cockroaches, they can't blame you for escalating to lice.

[txtriffidranch.livejournal.com]

I had a slight run-in with one of the bot larvae back when I was ten: our dog had one in her armpit, and my mother's yells when she saw what the dog was scratching at woke up the whole house. Considering that my mother worked as an ER nurse for a while, this is saying something.

[jolantru.livejournal.com]

Interesting...

[gigglingwizard.livejournal.com]

I'm puzzled. A few years ago, I took a class called "Forensic Aspects of Death Scenes." Half the class was mostly about searching for, exhuming, and analyzing corpses, and the other half was about collecting evidence in the forms of temperature readings, weather conditions, and samples of any insects present (making note of the stage they were in when collected).

The main insects we covered were blue and green bottle flies, black blowflies, and botflies. Why the hell did we cover botflies if they aren't planted on dead bodies? Unless we've got warm zombies crawling through rodent tunnels, you wouldn't think a bot fly could get on a corpse, at least not by the habits you've described here.

Is there another kind of bot fly in North America that reproduces differently, maybe?

[badnoodles.livejournal.com]

Hmm. That is unusual, as beetles are much more useful and prevalent at scenes of actual /death/ than bot flies, at least among humans in the United States. They can play a small role, though - younger bots may remain encysted because they simply aren't capable of leaving the host yet. Or the lesion may remain behind, even if the larvae itself is nowhere to be found.

More often, bot and other myiasi-inducing flies are important, legally speaking, in cases of abuse or neglect. I've never worked with bots, but I have worked on an elder abuse case where the caretaker allowed flies to develop on the skin of a helpless elderly woman.

[wirrrn.livejournal.com]

Bot Flies are awesome. I'm doing a presentation on them in January :yoinks picture:

[bellelvsbeast.livejournal.com]

I think bot flies and parasites in general are pretty cool...it's crazy what they will do to survive! I see maggots all day every day so they don't bother me....:)

[jhennara.livejournal.com]

i know this is kinda off topic. but what is the connection between cockroaches and lice? Perhaps its because i life in the "great white north" and dont have cockroaches up here but ive never heard about cockroaches and lice (and i took entomology and invertebrate zoology in university).

Hello.. Let's get acquainted...

[(Anonymous)]

Hi!
My name is Jessika!

freaked out

[(Anonymous)]

Can a botfly larve live without a host? My husband and son killed a rabbit only to discover this oversized dark grub thing on it. We did some research and discovered it to be a botfly. It fell off the rabbit and into the neighbors yard. Will it die? Also one was still on the rabbit, which is now dead and in my Oscar (trashcan) outside. Should I be concerned?

Re: freaked out

[urbpan.livejournal.com]

No the botfly larva cannot live without its host. Nothing to be concerned about--the botflies are always out there, so having one on the rabbit in the trashcan is no worse than having them living on the wild rabbits and other animals in your area.