Latest News from BPCA

12 November 2019

PestWatch: Pharaoh ants

Technical| PPC97 November 2019

Those in the industry for less than 10 years may not remember life before gel baits for controlling pharaoh ants (Monomorium pharaonis).

BPCA Technical Officer, Natalie Bungay, looks at treatments for pharaoh ants and how options have changed. 


It’s been some time since the first insecticide gel bait formulation (imidacloprid based) was released to add extra options for controlling pharaoh ants.

Before this release, the only option we had was s-methoprene insect growth regulators (IGR) which were, by their nature, slow acting.

How has this improved treatment options for professionals?

Biology and behaviour

As with all pest insect species, it is vital that we first recognise the need to keep ourselves up-to-date on biology and behaviour.

Our understanding of pharaoh ants allows our customers to have faith in our knowledge and associated promise to rid them of the insect infestation.

Getting to grips with the biology of the ants gives us the knowledge we need to ensure we target the insect in the right locations and we use the appropriate control methods.

Without knowledge of the pest species, we wouldn’t know how to control it professionally, legally and effectively!

Let’s have a bit of an update on pharaoh ants and their biology.

Location and habitat

The pharoah ant is a tropical species of ant only found in heated buildings in the UK.

Drawing from experience, popular areas to see reports of pharaoh ants are in bakeries at the side or near ovens or other machinery that lets off a fair amount of lovely heat!

But this isn’t to say that these obvious warm areas are the only locations these ants will head to.

There have been reports of the ants being found in hospitals and, more worryingly, within sterile surgical equipment.

The ant has a minimum breeding temperature of 18°c with the optimum being 30°C, which gives a good picture of both the origin of the name ‘tropical’ ant and of the preferred environments mentioned.

Reproduction and nests

pestwatch pharaoh ants bpca 5

The pharaoh ant follows a complete metamorphosis (egg>larva>pupa>adult) and, unlike some other ant species, the nest contains several queens, all of which lay eggs.

Queens have wings when they first emerge but these are soon lost, most likely because they are now unnecessary through evolution.

Nest sizes vary with no typical size being prevalent.

Nest size is dependent on available space which means they can grow to massive proportion with some research finding nests with 50,000 workers and 100,000 ants at young stages!

Eggs hatch in about one to two weeks and the resulting larvae are fed by the workers. Full larvae growth takes about three to four weeks, before they develop into pupae.

The adult ant will then appear in about two weeks making the complete cycle time, as an average, six to eight weeks.

The adult worker ants are wingless, about 4-5mm long and will live up to 10 months.

Workers provide food for the colony and maintain the nest.

Only 5-10% of workers engage in foraging, so those ants you see trailing down the face of a wall or machine are only a small piece of the picture!

In the event of a threat, workers can move pupae and young larvae away from the original colony.

This response to danger can be triggered if, for example, a pest technician wrongly decides to spray the trails or nests of ants which causes them to bud.

Budding is a known process by which the ants gradually spread throughout buildings or complexes. Pharaoh ants also do this deliberately to start new colonies.

General treatment overview

Tricky surveys

Successful control of pharaoh ants, as with most ant species, requires the destruction of nests.

This is often difficult to achieve because nests are often located in places such as voids and cavities, which can be inaccessible and tricky to survey visually.

The most effective control measures involve a thorough treatment so all the insects creating the infestation will be exposed to the toxicant in a short space of time.

Surveys must be conducted to determine the extent of the infestation, as not placing enough baiting points will ensure treatment failure.

Surveys should involve visual assessments and the collection of information about the distribution of ants from clients.

Additionally, a survey can be conducted by (regularly under-used) non-toxic baiting.

Baits may be based upon various materials including honey, sugar and meat (eg raw liver).


Once the extent of the infestation has been identified, the chosen bait can be applied.

We recommend that bait placement commences outside the infested area and progresses inwards until the whole area has been treated.

Care must be taken to ensure no pockets of infestation are missed during the treatment. Further surveys and customer liaison can determine the success of the treatment.

Back in the day

We’ve already mentioned that spraying the trails or nests of pharaoh ants is counterproductive and can cause more significant infestations.

When threatened, ants bud off to form new satellite colonies in new areas of the structure.

Back in the day, the only option was to bait, and the single available mode of action was an IGR, s-Methoprene, which is still available today.

When threatened, ants bud off to form new satellite colonies in new areas of the structure.

S-methoprene is a juvenile hormone equivalent; a substance that mimics a naturally occurring insect hormone.

This is mixed with a base bait and collected by the workers and fed to the larvae and queens.

This has the effect of sterilising the queen(s) to prevent further production of viable eggs and preventing developing larvae from reaching the adult stage.

Although workers are not directly affected, they will die off naturally (in 10-12 weeks) and not be replaced by succeeding workers, and so control of the infestation follows.

Dependent on the size of the infestation, full noticeable control could take four to six months.

This lengthy control period caused concern from customers who needed the issue to be controlled sooner rather than later but, unfortunately, it was the only real option.


S-methoprene is still available today and can be favourable in some situations, for example, anywhere with an organic rating which means the non-toxic formulation of s-methoprene would likely be the first call product.

In the last ten years manufacturers have made a great investment with the release of faster-acting compounds.

This means that rather than tedious control programmes that frustrate your customers, we now have a compound that will yield a visual reduction of pharaoh ants within a week.

Full control can be achieved in as little as two to three weeks.

A couple of days after baiting with these new active ingredients may result in you and your customer seeing more activity.

This is because the ants are drawn to it, because of highly attractive base formulations, so it’s a good sign!

Very quickly you will see favourable results.

Although we have this greater confidence and quicker reduction in ants, the complete control of the colony can take a little while (though not as long as four months).

It’s still important that you carry out a bespoke amount of follow-ups to ensure the colony has been wiped out and there are no remaining satellite colonies that have gone unnoticed.

And don’t forget...

I would disappoint myself if I did not remind our readers of one of my most popular phrases – always read the label!

Regardless of what you read or what you are trained to do, you must always read the labels of the products you use.

This is not only a legal requirement but labels and directions for use change on occasion, so you need to make sure you are following them.

Legality aside, labels affect treatment effectiveness. If you lay too much or lay too little, or apply it in the wrong places, it may cause treatment failure.

Save yourself time and money – read your labels!

Ask the team

Is there a specific pest species you’d like us to do an in-depth write up on? Let us know and we might just do it in a future PPC magazine.

Source: PPC97

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