Impurest's Guide to Animals #131 - Mydas Fly

Talk about things heating up, with temperatures expected to rise above thirty degrees it looks like I’m in for a sweaty few days out in the field. Last week’s issue, the tunnelling terror known as the Taita Hills Caecilian may thrive in such temperatures but ecologists certainly don’t. This week I decided to write this on the fly in the hopes of a buzz, hope you guys enjoy.


Issue #131 – Mydas Fly


Kingdom – Animalia

Phylum – Arthropoda

Class – Insecta

Order – Diptera

Family – Mydidae

Genus – Gauromydas

Species – heros

Related Species – The Mydas Fly is the largest of around 400 species found in the order Mydidae (1)

Range – Mydas flies are found in arid scrubland and dry grassland in Brazil

Fly in Wasp’s Clothing

Mydas flies are very large bulky black flies which reach a body length of 7cm, and are among the largest of all extant flies, with only the Timber Fly (Panthopthalmus bellardi) growing larger, and then only by about a centimetre. Despite their size, the adult Mydas fly is rarely seen due to its short lifespan in its imago form, which only lasts a few weeks and is mostly spent feeding on nectar.

During their short lifespan, the chance of predation is quite high, particularly since the adult Mydas flies are very large and slow fliers lacking the ariel agility of smaller members of the Diptera order. Despite this actual predation is low due to the adult Mydas flies mimicry of Tarantula Hawk Wasps from the genus Pepsis well-known for having a very painful venomous sting. The similarity to the wasp is so uncanny that the male Mydas Fly practices the same display behaviour of ‘hill-topping’ where he flies around the top of a leafcutter ant (Atta sp) hill to attract females to his position (2).

The Tarantuala Hawk Wasp, the species that the Mydas Fly mimics [2]
The Tarantuala Hawk Wasp, the species that the Mydas Fly mimics [2]

There is another reason for the flies choice of hilltopping venue, while the adults are herbivores, the larvae are active predators, not on the ants itself, but on the larvae of scarab beetles from the genus Osmoderma which feeds on deadwood that the ants use for growing fungi. From their subterranean lairs, the fly maggots may live for up to three years before pupating in readiness to emerge as a sexually mature imago many months later.

Ecology 101: An Introduction to Environmental Mechanics #15 – Bastian Mimicry

Mimicry is quite widespread across the animal kingdom, and can usually be sorted into one of four categories. Of these, all but one type are defensive in origin, and depending on what the animal is mimicking, is either considered crypsis (where an animal mimics a part of the environment), Mullerian Mimicry where two harmful species mimic each other or Batsien Mimicry where a harmless species mimics a harmful one. Of these three types of Mimicry, it is the later that is most well-known, thanks to several quite visual examples found throughout the Animal Kingdom.

Named after the English naturalist Henry William Bates after he discovered it while studying butterflies in the Amazon Rainforest, the species involved in the deception are known as the mimic and the model, with the later possessing a defensive quality that deters predators. Bates discovered that certain butterflies that resembled ones that were either toxic or tasted foul were largely avoided by birds, despite not possessing any kind of deterrent of their own.

Of the species that are considered ‘models’ for Batsian Mimicry, the Hymenoptera (Bees, Wasps and Ants) are some of the most commonly imitated. This is due in part to the swarming nature of such insects, often backed up by a venomous sting and in the case of ants a painful bite and the ability to spray acid. Looking like an ant or wasp is so advantageous that it has evolved multiples times in groups as diverse as flies, beetles, grasshoppers and jumping spiders. Some of the mimics have taken such deception that they can even fool the models they were imitating, with some jumping spiders using their disguises to infiltrate ant nests and predate on the larvae inside (3).


While rare, some species do mimic more than one species, with some of the jumping spiders mimicking multiple ant species throughout different parts of their lifespans. The species that imitates the widest range of models however is the Mimic Octopus (Tahumoctopus mimicus), which masquerades itself as many as fifteen different local species ranging from jellyfish to sea snakes and lion fish. In addition to such a wide range, the Mimic Octopus is an active mimic and morphs its shape to counter specific predators (4). For example, when attacked by a Damselfish (Family: Pomacentridae) the octopus morphs its body to resemble a Yellow Banded Sea Snake (Laticauda colurbina), a species that actively predates on small fish, and as such would be seen as an active threat to the attacking fish.

The Mimic Octopus (left) and it's various models (right) [4]
The Mimic Octopus (left) and it's various models (right) [4]

Very few other animals practice active mimicry, with bird species such as the Common Hawk-Cuckoo (Hierococcyx varius) mimicking the flight pattern of a similar sized bird of prey the Shikra (Accipter bandius) to avoid attack from other predatory birds. Such anti-predator defences aren’t fool-proof however, and the Hawk-Cuckoo may find itself under attack from crows and other bird species that won’t tolerate birds of prey in their habitat. In fact any species that mimics a deadly model may find that the success of its masquerade become too successful, with predators becoming complacent when they find out such mimics are harmless, or if a species evolves a counter to the defences of the original model.

One final example of well documented Bastian Mimicry has taken one interesting twist, which puts a new spin of how mimics and models evolve. The masquerade of the harmless Milk Snake (Lampropeltis triangulum) and its inspiring model the Eastern Coral Snake (Micrurus fulvius) is well known, and has even been featured in an earlier issue of Impurest’s Guide of Animals. Recent studies however have shed doubt on what benefit the Eastern Coral Snake gets from being colourful, since its venom is so toxic that it’s highly unlikely any predator would survive a bite to remember the visual cues associated with such a deadly predator. As such a third species, the mildly venomous False Coral Snake (Erythrolamprus aesculapii) was taken into account, which had long assumed to be a mimic of the more venomous species. It turns out that the Milk Snake is a mimic of a mimic, with the Eastern Coral Snake using the bright signals and more mild venom of the False Coral Snake to advertise its own toxins. This relationship between three unrelated snakes, has as such made scientists rethink and reclassify which species are Batsian Mimics and which ones are Mullerian Mimics (5).

The Eastern Coral Snake (Top), False Coral Snake (Middle Right) and the Milk Snake (Bottom) [5]
The Eastern Coral Snake (Top), False Coral Snake (Middle Right) and the Milk Snake (Bottom) [5]


1 -

2 - Alcock, J. 1987. Leks and hilltopping in insects. J. Nat. Hist.21:319-328.

3 - Nelson, X.J., Jackson, R.R., Edwards, G.B. & Barrion, A.T. (2006) "Living with the enemy: jumping spiders that mimic weaver ants". The Journal of Arachnology 33: 813–81

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5 - Goin, C.J.; O.B. Goin; G.R. Zug. 1978. Introduction to Herpetology, Third Edition. W.H. Freeman. San Francisco. xi + 378 pp. ISBN 0-7167-0020-4. (Mimicry in Erythrolamprus, p. 159.)

Picture References

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Well that’s a deceptively good issue even if I say so myself. Next week we’re making our own version of the Argo and heading out into open water. Until then make sure to critic, comment and suggest future issues as well as making sure you check past issues in Impurest’s Bestiary.

Many Thanks

Impurest Cheese

Want more IGTA? For the first part on this two part (so far) essay regarding mimicry featuring the Sinister Spider-tailed Viper, click here. Or for more foul flies, click here to see the terrible Toad Fly.