Aphids rounded up by ‘cowboy’ ants

What do cowboys and ants have in common? Well, apart from the ten-gallon hats, pickup trucks and that curious habit cowboys have of spontaneously shouting “yippee yi yo ki yay” at the line dance, ants probably have more in common with the old cowpokes than you might think.

I never really paid much attention to ants. Sure, these benevolent crawling critters can be annoying when they build their hills in the patio terrace and downright pesky when they get into your pants, but ants don’t usually cause damage to plants and can actually be beneficial as pollinators.

So a few years ago, when I noticed a steady stream of the creatures scurrying up and down the branches leading to the soft new growing tips of a Japanese maple – which had coincidentally become seriously infested with aphids – I thought a little reading was in order to find out what exactly was going on.

It turns out that just like cattle ranchers, shepherds and dairy farmers, some species of ants have the amazing ability to herd and carry aphids to the soft stems and shoots of plants and trees, where they nurture and protect these tiny sap-sucking insects from danger and predators. In return, the ants get a steady supply of their favourite food of honeydew, a sweet nectar excreted from well-fed aphids.

This remarkable symbiotic relationship becomes even more complex when you consider the lengths ants will go to farm their ‘livestock.’ Some will overwinter aphid eggs in their nest and take hatched nymphs to suitable ‘grazing’ areas as soon as the weather warms up in the spring. There, they corral them by using a chemical marker on their feet and clip the wings of maturing insects in the summer to keep them in place.

These aphids infested a spirea shrub in author Steven Chadwick’s front garden. PHOTO: Steven Chadwick
These aphids infested a spirea shrub in author Steven Chadwick’s front garden.
PHOTO: Steven Chadwick

Ants even have a way of milking these plant lice, by stroking the aphids’ backs with their antennae to keep the secretions of their captives ‘regular.’ And should a parasitic wasp or lady beetle try to horn in on the herd for a free snack, the ants will aggressively fight off the intruders and drive them away like shepherds protecting their flocks from wolves.

As fascinating as this insect farming activity is, large colonies of aphids don’t do much for plant health if they are not controlled, since the thick deposits of honeydew will seriously damage and deform new growth. Their voracious appetite and piercing beak can also disrupt circulation of phloem vessels and act as a vector to introduce viral and bacterial infections.

The simplest way to discourage their activity is to spray the bugs with soapy water. Next blast the stems and underside of the leaves with a strong stream of water from the garden hose and then prune out any infested areas that remain.

Of course dealing with a battalion of determined ants that want to raise their stock on a favourite tree or shrub means you have to block their access to the plants before they start to introduce a new herd. I have found that applying a barrier of reversed duct tape (sticky side out) around the base of the trunks and lower branches will usually deter them if it is replaced every couple of months. If you are successful in making it too difficult and not worth the effort for the little ant cowboys to farm on your favourite plant, instead of “yippee yi yo” they may squeak a rowdy “herd ‘em up and move ‘em out!” – and go somewhere else.


Steven Chadwick is a professional gardener and horticulturist, and longtime Beach resident

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