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Pharaoh's Ants, Monomorium pharaonis |
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Monomorium pharaonis, or pharaoh's ants as they are commonly known, are a common species of ant that can be found in urban environments around the globe. M.pharaonis originated in Central and West Africa though has managed to spread over the last century mainly due to the increase in international trade, because of this it is known as a tramp species. It has now established itself as one of the premier ant pests in urban environments; this is mainly due to its biology, aspects of which it shares with two other tramp species that are also considered major pests. The main concern with these species is their potential as a vector for disease when hospitals are infested as well as the general nuisance factor.
It is the biology of pharaoh's
ants that make it so aptly adapted to living in urban environments
as well as enabling it to extend to almost every corner of the
globe. Despite being a tropical species they manage very well
in colder climates through the advent of central heating.
M.pharaonis is a highly polygynous species i.e. there are many
queens within a single colony. Colonies are also polydomous (live
in multiple nest sites) forming a network of trails between nests.
These two aspects of pharaoh's ant biology mean that colonies
can reach mammoth proportions, for example being spread through
out the entirety of a multi-story hospital. This also makes an
infestation almost impossible to eradicate and enables pharaoh's
ants to spread prodigiously. A classic example of how large the
colonies of tramp species can become and how far they can spread
spatially is in the argentine ant, Iridomyrmex humilus. The largest
recorded colony in this species spreads from Portugal all the
way to Croatia and covers the majority of Italy, stretching across
a total distance of over 6000km. It has been proven that ants
from such remote locations are distantly related members of the
same enormous colony by a survey of their genes
Pharaoh's ants can reproduce in two ways. Firstly there is the
archetypal reproduction, where colonies produce males once they
reach sufficient size. The males, whose sole function in life
is to pass on their package of genes, then fly from the nest
and find another colony where they will mate with a queen before
dying. The second mechanism by which pharaoh's ants can reproduce
is by budding. This is an extension of the ant's polydomal behaviour.
If scouts find a new suitable nest sites and some workers migrate
to it along with either a queen or brood that is still totipotent
(i.e. could still develop into a queen) then a new nest will
be formed .If this is within a reasonable distance of the natal
nest there will still be an exchange of food and workers between
them as they still exist as the same colony. If the two domicile
become separated by an impassable boundary or there is an excessive
distance between the two nests, they will then operate as two
separate colonies and respond aggressively when they come into
contact.
Communication and Foraging Behaviour
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Like all ant species, pharaoh's ants use pheromones as their primary means of communication.The other modes of communication utilised by many ants are are tactile (touch), visual and stridulation (vibrational communication). Pheromones play a huge role in the organisation of foraging for pharaohs ants. One of the primary pheromones used is called a trail pheromone. This is laid down by workers as they walk by touching the gaster (the large posteria section of their body) to the floor. This pheromone induces other workers to follow it and allows trunk trails, like motorways, to be laid to new food sources. The process that pharaohs ants use to recruit foragers to a new food source is called Mass Recruitment, and is described in detail below. Other forms of recruitment used by other ant species include a primitive form called tandem running, where individuals follow the recruiting ant, and group recruitment when a few individuals follw the recruiter. The main advantage mass recruitment has over these simpler forms is that many more individuals are recruited in a far shorter span of time. |
| Mass Recruitment is a simple process by which workers can be rapidly allocated to a newly discovered food source in order to prevent competitors getting access to it, ensuring that the colony has the monopoly. The diagram on the left illustrates how it works. It is an autocatalytic (self-reinforcing) process governed by positive feedback mechanisms, ensuring a rapid build up of foragers. It also allows the allocation of foragers to remain dynamic and flexible. |
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