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The vast majority of ant species that are known pests pose a nuisance within homes and buildings, but a small minority can be medically and/or economically significant. For example, red-imported fire ants fit all three of these pest categories, as they inflict costly damage to residential turf-grass, inflict medically harmful stings that can be deadly to some individuals, and they are obviously a nuisance. Luckily, red-imported fire ants, and other highly venomous stinging ant species are largely absent from Massachusetts, with the exception of European fire ants. Surprisingly, several of the most commonly encountered ant pest species within homes can be medically threatening due to worker ants carrying and spreading disease-causing microorganisms. Numerous academic studies have shown that the following ant species carry and spread pathogens within structures: Pharaoh ants (M. pharaonis), pavement ants (T. caespitum), ghost ants (T. melanocephalum), little black ants (M. minimum), thief ants (S. molesta), and longhorn crazy ants (P. longicornis). All of these species are common household pests in Massachusetts, and most of them are the most commonly controlled ant pests in the country.

Pavement ants are one of the three most commonly managed ant pests in structures in the US, and they are the ants most frequently spotted skittering about on sidewalks and other paved surfaces. These ants invade homes to seek out foods, especially sweets, and they are often found infesting pantries. While pavement ants do not pose a public health threat, they can contaminate food, and workers are intermediate hosts of the poultry tapeworms Rail­li­etina tetrag­ona and Rail­li­etina echinobothrida. According to a 2012 study, Pharaoh ants and thief ants are the “two most common household pests of public health importance responsible for contaminating food and spreading foodborne pathogens.” These two pest species are the only ants featured on the FDA’s “Dirty 22” list, which is a list of all household pests (including rodents) that are significant for spreading food-borne diseases. Many studies have shown that Pharaoh ants, ghost ants, little black ants and longhorn crazy ants carry and spread numerous pathogens in indoor environments. In fact, all of these ants pose a disease threat within hospitals located throughout the world, particularly in South America and the United Kingdom.

One study showed that indoor Pharaoh ants and little black ants carry more pathogens than outdoor specimens of the same species. This same study found that Pharaoh ants and little black ants carry and spread the following strains of disease-causing bacteria within homes: Staphylococcus aureus, E. coli, Shigella sonnei, multiple strains of Streptococcus, and antibiotic-resistant Serratia marcescens, just to name a few. Ghost ants carry seven strains of disease causing bacteria, including Staphylococcus, Serratia, Klebsiella, Acinetobacter, Enterobacter, Candida and Enterococcus strains. In order to prevent ants from contaminating stored foods with pathogens, food should be kept in tightly sealed containers, and food storage areas should be regularly sanitized.

Have you ever encountered ants within stored food?