Harvester Ant — Pogonomyrmex spp.

Written for the trip rather than the house

This is the one page in this library that is not really about Whatcom County, and it is more useful for being honest about that.

Harvester ants are in the regional key to the key ant pests of the Pacific Northwest, and they deserve their place: they have one of the very few genuinely severe stings among ants in this region. But the extension guidance is equally clear about where they are, and it is not here. The greatest number of colonies occurs along the Columbia and Snake river areas — the dry side of the state, where the soil suits them. Both halves of that are set out in PNW 624, the WSU Extension ant key covering Washington, Oregon and Idaho.

So this page exists for two readers. Somebody heading east to camp, fish, boat or work, who ought to know what a cleared circle of bare sandy ground means. And somebody who has found a large reddish ant here and wants to know whether that is what they have, which it very probably is not.

Recognizing them

Size. Six to eight millimeters, monomorphic. Large, and all one size — no mix of big and small workers in a trail.

Color. Reddish or reddish brown in most species.

The psammophore. This is the feature nothing else here has, and it is genuinely visible with a hand lens. A fringe of long hairs beneath the head that looks unmistakably like a beard. It works as a basket for carrying loose soil out of a burrow, which is why an ant that digs in sand has one and an ant that digs in loam does not.

If you can see the beard, you have a harvester ant.

The nest, and what it looks like from a distance

The nest gives itself away long before the ants do.

Harvester ants clear vegetation from a circle around the entrance, sometimes a substantial one, leaving a disc of bare ground with a hole in the middle. Frequently there is a scattering of small stones, and chaff — the discarded husks from the seeds they have processed — around the opening.

That bare disc in otherwise vegetated ground is the thing to notice, and it is the practical safety cue. In open sandy country on the dry side, a cleared circle is worth walking around rather than sitting on.

They nest only in sandy soil of a particular texture, which is the reason the distribution is what it is. That specificity is unusual even among ground-nesting ants, and it means the species does not simply spread wherever it is warm enough.

The sting

This is the reason the species matters at all, and it is worth stating without either exaggerating or downplaying it.

The extension guidance describes a harvester ant sting as rather severe, somewhat like a honey bee or yellowjacket sting. In a region where most ants either cannot sting a person effectively or produce nothing worse than a momentary nip, that puts them in a very small category.

It is not, in the ordinary case, dangerous. The guidance is measured about this too: it is usually not a serious pest, unless there is an allergic reaction, and few people are stung.

The two circumstances that change the picture are the ones that always change it. A person with a known allergy to insect venom should treat a harvester ant the same way they treat a wasp. And multiple stings — from kneeling or sitting on a nest rather than encountering one ant — are a different event from a single one.

Where people actually get stung

The guidance is unusually specific and it is worth quoting in substance: people who are stung are usually engaged in picnicking, fishing, rockhounding or other recreational activities.

That is a precise description of the risk. It is not a household hazard. It is what happens when somebody sits down on a river bar, spreads a blanket on open sandy ground, kneels to sort rocks, or sets up a chair without looking at what is underneath it.

Which makes the prevention obvious and free. In open sandy country east of the Cascades, look at the ground before you put a blanket, a chair, a cooler or a child on it. A cleared circle with a hole in it is a nest, and moving ten feet is the whole of the mitigation.

Seeds, and why they are called harvesters

They collect seeds — mostly of grasses and various weeds — carry them underground, and store them.

That is genuinely unusual behavior and it explains almost everything else about the species. The chaff around a nest entrance is the discarded husk after processing. The bare cleared circle keeps competing vegetation away from the nest. The psammophore exists to move sand out of the tunnels the stores are kept in.

It also makes them ecologically significant in dry grassland rather than a straightforward pest. They redistribute seed, they turn soil, and in most settings where they occur they are simply part of how that landscape works.

Where they are a genuine agricultural problem

One specific case, and it is a good example of a pest being a pest only in context.

The extension note mentions that harvester ants can be a problem in alkali bee beds. Those are managed nesting grounds — engineered beds of salty soil — maintained in eastern Washington to support alkali bees, which are used as pollinators for alfalfa seed production. It is a highly specialized bit of agriculture and the beds represent significant investment.

Harvester ants moving into that ground are a direct conflict with a managed pollinator operation, and that is a real problem for the growers concerned.

For everybody else, it is a useful illustration: the same ant is a neutral part of a grassland, a hazard on a picnic site, and a genuine agricultural pest, all depending on whose ground it is on.

What you probably have instead, here

Somebody in Whatcom County looking at a large reddish ant is much more likely looking at one of these.

Thatching ant. Large, four to nine millimeters, frequently bi-colored red and black, with a notch in the thoracic profile. Builds a mound of grass and plant material rather than clearing a bare circle. Bites and sprays formic acid rather than stinging. This is by far the commonest answer here and it has its own page.

Carpenter ant. Large, usually black, evenly rounded thoracic profile, nests in wood. Does not sting.

Pavement ant. Much smaller, 2.5 to 3 millimeters, with fine parallel grooves on the head and thorax, and piles of excavated sand along paving. Can sting, mildly, usually only if trapped against skin.

The quick sorting question is the nest. Mound of plant material: thatching ant. Galleries in wood: carpenter ant. Sand piles on a patio: pavement ant. Bare cleared circle in sandy ground with chaff around it: harvester ant, and you are probably not in Whatcom County.

If you genuinely have them here

It is not impossible — the guidance says various species occur throughout the Pacific Northwest even though the concentration is eastern — and the response would depend entirely on where the nest is.

On open ground nobody uses, nothing. The species is not damaging anything and the sting only matters where people are.

Where a nest is in ground that people actually use — a play area, a path, a camping spot, a work area — that is a real conflict and one of the cases where treating a nest directly is warranted. Direct treatment of the nest rather than a broadcast application, because a broadcast treatment of open sandy ground for one colony is disproportionate.

And in either case the first step is confirming the identification, because almost every large reddish ant reported here turns out to be something else.

What we will not sell you

We will not treat a large ant because it is large. That is the same principle this library applies to the great golden digger wasp, and it holds here: size is not a hazard signal, and the ants in this region that genuinely warrant caution are identified by what they are rather than how big they look.

We will not tell a Whatcom County customer they have harvester ants without a specimen. The distribution makes it unlikely and the thatching ant makes it easy to get wrong.

We will not treat open ground on a rural property for a species that is part of the landscape and not in anybody’s way.

And where somebody is worried about a trip east rather than about their own yard, the useful answer is free: look at the ground before you sit on it.

Why it is in a Pacific Northwest key at all

Somebody reading this page in Bellingham might reasonably ask why a mostly eastern-Washington ant sits in a publication about the whole region, and the answer is instructive about how these guides are built.

The key covers Washington, Oregon and Idaho, and those three states contain a great deal more dry country than wet. The Columbia Basin, the Snake River plain, central Oregon and southern Idaho are all harvester ant country. From that perspective this is a widespread and significant regional species, and the wet strip west of the Cascades where this company works is the unusual part.

It is a useful corrective. The species list a pest control company works from is shaped by its own geography, and it is easy to assume the local set is the regional set. It is not, and a customer moving here from eastern Washington frequently arrives with a mental list of insects that does not match what they will meet.

The reverse holds too. Somebody moving from here to Yakima or the Tri-Cities will meet ants this county does not have, and this is one of them.

The sting compared with what people know

Since the guidance compares it to a honey bee or yellowjacket sting, the comparison is worth extending, because most people calibrate insect risk from those two.

A honey bee stings once and dies, and the sting is a defensive act by an insect protecting a colony. A yellowjacket can sting repeatedly and will pursue, which is what makes a disturbed ground nest genuinely dangerous.

A harvester ant is closer to the first than the second in outcome and closer to neither in circumstance. It is not defending a colony against an intruder in the way a yellowjacket does, it does not pursue, and encounters are almost always a single insect on a person who has sat down on its ground.

The practical difference is that a yellowjacket nest can turn a mistake into thirty stings in ninety seconds. A harvester ant nest, in the same circumstances, will not.

That does not make the individual sting mild. It makes the event containable, which is the more useful thing to know when deciding whether to worry.

What to do if you are stung

Since the guidance compares it to a bee or wasp sting, the response is the same as for those, and it is worth setting out plainly for somebody who has just had one on a river bar with no phone signal.

Move away from the ground you were on, because where there is one there is a nest, and standing on it produces more.

Wash the site. Cold water or ice for the pain and the swelling.

Watch the person rather than the sting. A local reaction — pain, redness, swelling around the site — is ordinary and resolves. What matters is anything away from the sting site: difficulty breathing, swelling of the face or throat, widespread hives, faintness. That is a systemic reaction and it is an emergency regardless of what caused it.

Anybody with a known insect sting allergy should be carrying what they normally carry, and should treat this as within scope rather than assuming an ant does not count.

None of that is specific to harvester ants. It is the standard sting response, and the point of including it is that people apply it to wasps and frequently do not think to apply it to an ant.

For anybody working out there

Field crews, surveyors, utility workers, agricultural staff and anybody else spending working days on dry open ground in eastern Washington have a slightly different exposure from a family on a picnic.

The mitigations are the same and the discipline is what changes. Look before kneeling, before sitting, before putting a bag down, and before setting up equipment. Mark nests where a crew is working the same ground for days. Treat a cleared circle the way you would treat any other ground hazard on a site.

For a crew leader, that is a two-sentence toolbox item, and it is worth having because a stung worker on open ground a long way from a vehicle is a disproportionate problem relative to how easily it is avoided.

The identification service, applied to this one

Since almost every report of this species in Whatcom County turns out to be something else, this is one of the pages where the free identification does the most work.

A photograph is usually enough for an ant this size, which is unusual — most of the ant pages here ask for a specimen because the characters are too small to photograph. At six to eight millimeters, with a beard under the head and a distinctive reddish color, a decent close-up settles it.

What to capture: the whole ant in frame, from the side if possible, with something for scale. If there is a nest, a photograph of the ground around the entrance, because a cleared bare circle and a thatch mound look nothing alike and the nest identifies the species faster than the insect does.

Send it and we will tell you what it is. In this county the answer is very likely to be a thatching ant, and that is a much easier conversation.

The short version

Large, reddish, all one size, with a fringe of hairs under the head that looks like a beard. Nests only in sandy soil, in a cleared circle of bare ground with chaff around the entrance.

One of the very few ants in this region with a sting worth respecting — the regional guidance compares it to a honey bee or a yellowjacket — and almost nobody in Whatcom County will ever meet one, because the colonies are concentrated on the dry side of the state.

If you are heading east to camp, fish or work on open sandy ground, look at what you are about to sit on. If you are looking at a large reddish ant here, it is much more likely a thatching ant, and that page is the one you want.

Why we wrote this page at all

A pest control company that works one wet county in the far northwest corner of Washington has no commercial reason to publish a page about an ant its customers will almost never encounter.

It is here because the library is built from the regional extension key rather than from our call log, and the key covers the whole Pacific Northwest. Leaving out the species that do not generate revenue here would make it a marketing document rather than a reference, and it would remove the one entry that explains what a genuinely severe ant sting looks like in this region.

It is also here because people move, travel and work across the state, and the question “is this the one that stings badly” deserves an answer that does not depend on which side of the Cascades somebody happens to be standing on when they ask it.