In June of 2004, I was poking around in our backyard garden in Tucson, Arizona. The squash plants were flowering, and I was having fun looking at their enormous flowers. I noticed that that some of the flowers were being visited by red-and-black ants.
These ants were Dorymyrmex bicolor, an ant that was very common in our yard. Dorymyrmex bicolor is an member of the Dolichoderinae – an ant subfamily that doesn’t have stings, but rather can release a fruity/unpleasant odor from their anal gland when they wish to do so. I think the chemical must be especially unpleasant for creatures that are closer to the same size as Dolichoderine ants – other ants have a notably negative reaction to the odor.
These ants would nest in open areas of our yard. Sometimes they’d nest at the edge of large rocks, but more often just out in the open gravel. They were very common.
And they seemed to love sugar. If there were leafhoppers or aphids excreting sugary honeydew, there was a good chance that Dorymyrmex bicolor would be tending the aphids. If there were active extrafloral nectaries on some of the plants in our yard, Dorymyrmex bicolor would be all over it.
They reminded me a lot of sugar-addicted toddlers, running around trying to get their next fix of simple high-fructose corn syrup.
So what were they doing on the Squash blossoms?
As I watched the ants, I saw that the ants that were going into the flower had ‘normal’ looking gasters (abdomens) – they were the usual ovoid shape, and the armour-plate tergites and sternites of the gasters were touching or overlapping.
The ants that were coming out of the flower, though, had gasters that were so distended that the membranes between the tergites were stretched out. The ants’ gasters were as swollen and distended as raisins that have been soaking in water.
As I looked into the squash flowers, I could see that the ants were clustering around the bases of the flower stigmata. Ah – there were nectaries there, and the ants were drinking the nectar.
The nectaries produce sugar for the Squash pollinators, often a type of bee. The bee has to brush against the stigmata and gets covered in pollen as it tries to get at the nectaries. Then the bee flies to another flower, and the pollen gets transferred.
I’d not seen this before, but the nectaries in the Squash blossoms were almost like little mading pools full of sugary syrup. The ants were gorging on the nectar.
I would be surprised if Dorymyrmex bicolor is a significant pollinator of the Squash flowers. I only saw a couple of instances where the workers were carrying pollen grains.
I would also expect that if a pollinator such as a Squash Bee did arrive, it would have to compete with the ants for the nectar.
I wonder if the ants do depress pollination of the Squash blossoms. We certainly didn’t get a lot of Squash out of our garden 🙂
