Alouattamyia baeri

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Gabrielle Keaton and it is about a nasty botfly that lives in the neck of howler monkeys (you can read the previous post about picky bat flies that live on bats here).

Photo of botfly pores on howler monkey neck from Plate 1 of this paper

You know how itchy a mosquito bite can be - you scratch it then a lump forms. Imagine that lump forming but not going away. Instead, it grows and grows inside of you until finally a black grub plops out of a hole in your neck onto the ground. Well that’s what it’s like for the howler monkeys of Panama!

This nasty parasite in this case is the larvae of Alouattamyia baeri, a botfly that lives on free-ranging howler monkeys (Alouatta palliate). In a study conducted over seven years from 1987 to 1993, researcher Dr Katherine Milton investigated a variety of factors relating to this parasite's life cycle including its infection prevalence and intensity. She found that 60% of the howler monkeys on Barro Colorado Island (BCI) were infected by this botfly.

Alouattamyia baeri are large (18 to 20mm in length) black flies. The adult fly sounds and look like neotropical bees. When flies that were collected from the howler populations on BCI were reared in captivity, it was found that female flies produced an average 1400 eggs each, laid in discrete rows. These eggs required the appropriate stimuli (carbon dioxide and heat) to hatch into parasitic larvae that then invade their host through the nose and mouth where it migrates to the neck and opens a up larval pore. The larva reside in the howler’s neck for approximately 6 weeks, passing through 3 instars (developmental stages). After this, the larva drops out of the monkey's neck warble and burrows into the soil where it finishes the last developmental stage underground.  The study found that the entire life cycle takes approximately 13 weeks.

Dr Milton discovered that most of larval growth (86%) occurs during the 3rd instar when its food consumption increase by about 20%. This means the larva was trying to extract the most resources at the last possible moment of its stay, so if it ends up killing the host, it wouldn't matter to them because they are out of there.

Infestations were the highest during the wetter seasons and these periods also strongly correlated with peaks in the monkey’s mortality. Monkeys carrying the botfly larvae lack subcutaneous fat reserves. As if having a 2.4 centimetre long and 1.5 centimetre wide maggot in your neck wasn’t bad enough, even after the botfly has made its exit, the hole they made in their host remains open for several days. That’s pretty like much waving a neon ‘vacancy’ sign in front of the primary screw worm fly (Cochliomyia hominivorax) - an even nastier parasite that lays its eggs in open flesh wounds. When the screwfly larvae hatch, they feast on anything and everything surrounding that wound. Some monkey cadavers were even found with hands eaten down to the bone from these nasty little maggot and at least half of the C. hominivorax infestations found on howler monkeys were the result of prior A. baeri infections

Now, I’m sure you might have a bit of a panic next time you feel a little raised bump hanging around your neck, but remember - even if it is a botfly, at least you know it will be gone in 6 weeks' time.

References:
Milton, K. (1996), Effects of bot fly (Alouattamyia baeri) parasitism on a free-ranging howler monkey (Alouatta palliata) population in Panama. Journal of Zoology 239: 39–63.

This post was written by Gabrielle Keaton