by Tomer Czaczkes
Based on research for the paper “T.J. Czaczkes and P. Kumar. In press. Very rapid multi-odour discrimination learning in the ant Lasius niger. Insectes Sociaux.”
Most people are shocked to hear that ants can learn. While the readers of this blog are probably not surprised by this, quite how good they are might come as a surprise – it certainly surprised me! In our recent study, Pragya Kumar and I found that Black Garden ants (Lasius niger) can learn at least two (most likely three) odour-sugar associations, having only experienced each combination twice. They can learn one association in just one visit.
The joys of comparative psychology:
Let’s unpack that: we were exploring discrimination learning, where the ant has to learn that one odour (e.g. rose) means very sweet sugar water, another (e.g. lemon) quite sweet, another (e.g. lavender) slightly sweet, and another (e.g. blackberry) just a teeny bit sweet. If the ant learns successfully, she should prefer rose to lemon, and lemon to lavender. They should never prefer blackberry when one of the other options is available. So, we let individually-marked ants up a bridge to find a drop of flavoured sugar, then let her go back to the nest, and when she came back for a second visit she found another drop with a different taste and a different sweetness. After she’s experienced each combination once or twice, we give her a choice on a Y-maze: for example, does she follow the arm which smells like lemon, or the arm which smells like lavender? By the way, the methods are all published in another Insectes Sociaux paper (Czaczkes, 2018). And if you have a 3D printer, you can print your own mazes too.
Ants made mostly correct decisions, even if they only experienced each taste/quality combination once. Clever ants! So… why did I say that ants can learn “at least two” combinations? Well, we simply can’t be sure of more.
Consider our situation: Rose > lemon > lavender > blackberry. Firstly, they didn’t prefer lavender to blackberry. So, we’re down to three. Now, imagine that the ants never learned the second worst smell (lavender). What would her decisions look like? It would still prefer lemon > lavender, because lemon is better than nothing. So, we’re down to two we can be sure of. Now, we’re pretty sure they learned lavender, but we just couldn’t prove it in this setup!
This, to me, is the joy of comparative psychology – every experiment is like a logical puzzle, where evidence builds up, ruling out alternative explanations, until you run out of alternatives (or evidence). I admit, it’s hard work – or, at least, I find it hard. Sometimes I feel my brain creaking under the pressure. But it’s also very rewarding, when you’ve lined up your evidence, and can knock the alternatives out. Even finding the logical holes is fun, as happened in this experiment!
Back to the ants
So, L. niger ants can learn quite a lot, and fast. Why is that interesting? Firstly, it’s perhaps surprising, given how small their brains are. But enough e-ink has been spilled on this topic. More practically, this opens the door to performing complex training regimes and tests. A lot of psychological research involves asking the question: “which option do you prefer, A or B? How about C or D?”. Because we cannot simply ask animals, we have to train them to associate each option with a cue, and then see which they prefer. So, for example, we can ask if ants like to gamble by teaching them that lemon is a risky smell, but rose is a safe smell. Being able to quickly train ants to complex option sets can open the door to a much deeper understanding of how ants think, what they like, and how they make decisions.