by Matthew Cobb
It is a truth universally acknowledged that any communication system can be hijacked and exploited by an external party. I came across this great example from 2009, published on Alex Wild’s old blog PhotoSynthesis, which includes the weirdest antennae I have ever seen in an adult fly.
Many ants (and other social insects) will feed each other by a process known as trophallaxis. Typically, one individual will come up to another, touch antennae – presumably involving an exchange of chemical signals, but vibration may also be involved – and the ant with food will then give up some of its precious booty to its sister. Here’s one of Alex’s pictures of two Crematogaster ants doing this in KwaZulu-Natal, in eastern South Africa:
Alex noticed that the trail of ants going up an Acacia tree was being buzzed by some small grey flies. His photos revealed what as going on. The flies – which turn out to be a species called Milichia patrizii – were hacking the ants’ communication system and stealing food – ‘kleptoparasitism’. The flies would grab the antennae of the ant, and then stick their proboscis into the ant’s mouth, whereupon the ant would give its food up. All the fly has to do is hang around and get some free grub (sorry).
Here’s a great pic. See if you can see *how* the fly is grabbing its victim’s antennae:
Look closely – the fly is holding the ant’s antenna in between its own antennae! Alex writes:
The fly triggers an automatic regurgitation response by tapping the ant’s palps with her proboscis. Oddly enough, once the ant has acquiesced the fly releases her victim’s antenna and the ant just sits there. There may be a chemical communication going on between the tip of the ants antennae and the concave upper lip of the fly, but we don’t know. Might be a project of interest to a South African student. If any are reading this. Hint, hint, hint.
The ability to Milichia patrizii flies move their antennae in this way is unique, it appears. It would be interesting to know if related species show similar moveable appendages, or if M. patrizii has evolved them at the same time as it began to hack the ants’ communication system.
Although, like Alex, I would bet on there being an unseen chemical element to this behaviour, it’s possible that their ‘hack’ isn’t quite so complex. Some ants will grab hold of each other’s antennae in dominance struggles. The ant may simply be feeling subdued, and will then give up its food in a reflex action, not because it has been totally duped into ‘thinking’ it’s feeding a sister. Separating these hypotheses would be difficult, I suspect, but an initial test would be to immobilise a Crematogaster ant, and then tickle its mouthparts and see whether it gives up its food. That would indicate that food release did not require chemical camouflage on the part of the thief.
Milichia patrizii was first described in 1952 by Willi Hennig, the Swiss biologist who developed the use of what is known as cladistics to study relationships between organisms. He was also a great maggot man. But he didn’t see M. patrizii in the wild, and no one knew of this behaviour until Alex noticed it, and called it the ‘ant-mugging fly’ on his blog (a common name which has now been taken up by the Natural History Museum in London), although this is not particularly violent ‘mugging’.
Hennig studied a preserved, dead specimen, on which the antennae do not look particularly unusual, and certainly not as though they could grab anything.
Alex published an article about his discovery with Irina Brake in African Invertebrates, but I haven’t been able to read it as that particular issue is not on line at the moment. For more details, you should read Alex’s original post.
The observant among you may have noticed that I referred to the weirdest antennae I have seen on an adult fly. Michael Skvarla on Twitter pointed out that phantom midge larvae, which live in the water, have antennae that can grab, too, but it a particularly predatorial fashion. Here’s a picture from vernalpool.org (the silver blobs are air bubbles that the beast uses as it moves up and down in the water):
Do any readers know of any other antennae in flies that are used in weird ways?
Live action photos © Alex Wild. Dead fly photo (C) NHM. Midge larva – it says.
H/t to the Twitter folk who were tweeting about various raptorial appendages in flies (raptorial mid-tarsae? amazing) in the wee small hours of Sunday morning and gave me the links and the inspiration: @BioInFocus @dllavaneras @phil_torres @MSkvarla36 @flygirlNHM @BrytheFlyGuy
I’m fairly sure Willi Hennig was German – he worked in Berlin and Stuttgart, and opponents of cladism sometimes vilify him as a Nazi.
I knew I should have checked that. Let’s leave Hennig, like Schrödinger’s fly, both German AND Swiss until someone can be bothered to find out for certain.
That is an amazing picture of the midge larva.
Your mention of cladistics spurs me to mention that Darwin was there first, in a sense. I’ve been browsing the first edition of On the Origin of Species, and in the final chapters Darwin went on at great length about the necessity of aligning taxonomy with genealogy. Of course, he had nothing even remotely resembling modern DNA analysis, but that’s the core of cladistics, so “genealogy” (his word) depended on physical features.
Yes, there is a sentence in the Origin that can be understood as a suggestion to classify organisms by relatedness:
If we extend the use of this element of descent, – the only certainly known cause of similarity in organic beings, – we shall understand what is meant by the natural system: it is genealogical in its attempted arrangement, with the grades of acquired difference marked by the terms varieties, species, genera, families, orders and classes.
The funny thing is, despite this “evolutionary” systematists, i.e. the opponents of phylogenetic systematics, also claim that Darwin would have been on their side.
Reblogged this on Mark Solock Blog.
Hennig was German.