You wouldn’t think there would be much to attract ants to a cactus. They have waxy stems covered with spines.
There is one structure in this photograph, however, that is highly attractive to ants.
Do you see it yet? No, it isn’t the clusters of extrafloral nectaries.
It’s a bud.
What are the ants doing?
In case you aren’t familiar with the relationship between ants and cacti, the ants are visiting to obtain a sugary liquid produced by the plant. It would appear that the softer, quickly growing tissue of a bud is more susceptible to being eaten by plant-feeding caterpillars or beetles. It is likely the ants will defend their free “soda fountain” and chase these sorts of pests away.
Those of you who have seen extrafloral nectaries on cacti, do you agree that those yellow bulges between the spines above the bud are extrafloral nectaries?
Here’s an ant visiting an extrafloral nectary on a barrel cactus.
Any ideas why the two separate structures?
Interesting that the ants are the Old-World-origin, tramp species Paratrechina longicornis, demonstrating the near universality of the nectary-tending habit among ants, even those that have no evolutionary history with these particular plants.
That is a very good point.
I have a beautiful cactus in full flower – but ants are attacking – and the blossom and buds are falling off.
Can you please advise me how to deal with this infestation.
Fran Cavell
Fran,
Actually it is much more likely that your buds and blossoms are falling prey to another insect or animal. The ants have a special association with cacti, whereby the cacti produce nectar for the ants in return for protection and other services. The ants are there to defend the buds and blossoms, but obviously they are failing. I would recommend visiting the cacti at night with a flashlight, because your culprit is likely active when the ants are not present.
Thank you Roberta. I was given this beautiful plant a few weeks ago – and looked up in gardening book how to look after it. Gave just a little water – and it was fine. Couple of weeks later – a half cupful water – and then the flowers became slimy and unwell. Do you think I have watered too mud? I am desolate – I love it so much and want to help it to recuperate! I appreciate your help Roberta
Regards
Fran
Fran,
Well, my local cactus expert says that watering a cactus too much can cause it to drop its flowers. He advises letting it dry out.
Good luck!
Thank you so much Roberta. Will try that and grateful for your input. Thank your local cactus expert for me!
Regards
Fran