It’s stunning 4.5 years ago, in one of my first stories for picmybug, that I wondered why the heck weaver ants bite my wife but not me. Read that story here, it might be lactose related!
After some posts about ant-mimicry in spiders, now I’m finally back to ants. Camponotus compressus is only the second ant species on picmybug, and again it is about sugars.
The common black ant, if my photo ID is correct, doesn’t do what it’s supposed to do in the Maldives. I usually see them around cat food. Or garbage. They are also the first when it comes to carcasses. Huge, impressive ants, more massive than weaver ants, with the typical running-around-temperament. At night they become more weaver-antish, when they sit on walls while actively watching the environment.
C. compressus was described by the Danish zoologist Johann Christian Fabricius in 1787. He described roughly 10.000 other animals as well. Ants belong to the order Hymenoptera, together with wasps and bees. In the family Formicidae are 16 subfamilies, and a total of 345 genera.
What I did not observe in this species in the Maldives, but is often described (from Pakistan), is trophobiosis. This species of ants is described as being in favour of honeydew, the sweet liquid that some hemiptera, like aphids, produce. And that’s actually my story, because I always wondered. Why do ants wait for honeydew from aphids. Why do they make an effort to protect the aphids. Why don’t they just cut the plants themselves and drink the sap?
What’s sap, and what is honeydew, if it’s not just the sap aphids are sucking from plants. Couldn’t ants directly drink the sap as well?
It is a complex topic, no surprise, because there are approximately 80.000 species of hemiptera, probably over 14.000 species of ants, and nearly 400.000 species of plants on earth. That makes 448 trillion combinations. Plus, sap and honeydew contain a mix of several sugars, minerals, aminoacids, and more.
So why is the aphid-security-business for ants more attractive than sap-slurping?
The answer I found is osmosis. My source is mainly Fischer & Shingleton 2001. Actually osmosis is the challenge aphids face. And melezitose is perhaps (partially) the solution. The thing is, you can’t just eat as much sugar as you want. Especially when you are an insect. An aphid that is full with glucose or fructose, would be subject to strong osmotic pressure. That means water would automatically and inevitably penetrate into the insect. Until it pops. Like ripe fruits pop when it rains. You witness osmosis the other way when you put salt on cut eggplant. Water will migrate out of the vegetable. It seems aphids take in lots of sugar, while extracting important, lower-concentrated ingredients of the sap. To solve the osmosis issue, they turn simple sugars into a higher molecular saccharide called melezitose. So aphids can store more sugar by converting it into melezitose. Interestingly the melezitose attracts ants, and a lack of it makes the honeydew unattractive for ants. What I could not find out is why ants are attracted to melezitose.
Ants might have the same osmosis issue, and they solved it by drinking melezitose rich honeydew.
Maybe osmosis is the main reason for melezitose production. Or is it the ant-attraction, in return for protection and care? That might be a chicken or egg situation I guess. This example of trophobiosis remains a bit of a mystery to me, and perhaps also to the rest of the curious world. Not all hemiptera produce melezitose, and those who don’t are much lesser attractive to ants.
It is also melezitose that turns honey into cement honey. Did you know that forest honey comes from honeydew, which bees collected from hemiptera? In 2024 a ‘cement honey crisis’ concerned beekeepers in Switzerland and surrounding areas. The fast crystallisation makes harvesting difficult, for humans as well as for the bees.
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