LIFE CYCLE

  Formica ant species, like other ants with complete metamorphosis, pass through four stages during their life cycle. These stages are known as the egg, the larva, the pupa and the adult. Eggs of Formica species are tiny, ellipsoidal to elongate-ellipsoidal in shape, of whitish colour and with a thin transparent shell.

  Eggs hatch into larvae and they are soft white translation grubs without legs. The distinguishing shape of the larva is that of a crook-necked squash with the posterior part and straight; the anterior end is more slender and curved ventrally. On the anterior end is a small head bearing the chewing mouth parts; antennae are reduced to a pair of low bumps. There are no eyes in the larval stage. The larval body has thirteen segments more or less clearly separated by constrictions.


  The larval stage is the period of growth of ants. The hatched larva is barely larger than the egg. The larva feeds, moults several times and grows. However, they don’t have eyes or major organs and are limited to opening their mouths and wiggling. The worker ants or queen will help to feed them.

  After several moults in several weeks, pupal structures start to develop inside the larval skin. The last larval form is named as a semipupa. When its skin is shed, the creature is known as a pupa. The pupal stage is the period of transformation to an adult. During this period, adult structures develop inside the pupa. When the pupal skin is shed an adult ant emerges. It is pale-coloured and soft bodied. It takes several days for the integument to harden and the colour to darken.

  If a cocoon is to be spun, this is done by the larva just before it becomes a semipupa. Larvae cannot be spin cocoons until they buried in the soil or covered with detritus by the workers. As soon as the cocoon is finished, the workers unearth it and clean off all debris from the outer surface. If no cocoon is spun, the pupa is said to be naked. The Formica ants have it both ways: naked pupae and cocoons may be found in the same nest at the same time.

  The length of ant's stages is highly variable and dependent upon temperature. In temperate climates, like in Manitoba, development is naturally happening during the summer. In an inactivate state of many species larvae or pupae will overwinter.

( Wheeler and Wheeler, 1963)

THE SEASONAL CYCLE

As the temperature decreases with the entry of winter, ants become more inactive and gather in the deeper chambers of their nests. Their tissues changed in such a way that the freezing point is dropped. The ants then pass the winter in dense torpid clusters. Little or no heat is generated by their muscular activity. Naturally no food is consumed in the tropic state of ants. In the spring, the autumnal process is reversed: the ants become gradually more active with the gradual warming of the soil. Summer months are the months of greatest activity among ants in temperate regions as in Manitoba.

( Wheeler and Wheeler, 1963)

THE COLONY CYCLE

           
  • Photo Credit: Alex Wild
  • Once the ant colony has become well established it begins producing winged sexual forms. At the right season and the right time of day and under suitable meteorological conditions, a mating flight of winged males and females (queens) may occur. The requirements differ with the species; ants from many nests of the same species may fly simultaneously. Avoiding inbreeding and dispersing the species are the main purpose of this mating flight. In some species there is no mating flight and their copulating occurs either on the ground or on vegetation.

    After copulating, the couple separates and the male soon dies. The female breaks off her wings (deälate female). The deälate female searches for a cavity under a stone or under bark, or digs a small hole in the soil.

    Wheeler (1923, p. 161-162) says: “As soon as the egg mature, they are laid and the queen nurses the hatching larvae and feeds them with her saliva till they pupate. Since she never leaves the cell during all this time and has access to no food, except the fat she stored in her abdomen during her larval life and her dissolved wing-muscles, the workers that emerge from the pupae are all abnormally small. They dig their way out throughout the soil, thus establishing the communication between the cell and outside world, collect food for themselves and their mother and thus enable to lay more eggs. They take charge of the second brood of eggs and larvae, which, being more abundantly fed, develop into larger workers. The population of the colony now increases rapidly, new chambers and galleries are added to the nest and the queen devotes herself to digesting the food received from the workers and to laying more eggs”.

    The method of colony-founding described above might be considered the standard method. However, there are several other procedures may be followed by certain species.
    ( Wheeler and Wheeler, 1963)

    ANT POLYMORPHISM

                                                                                                                                                                                                                                                                                                    Photo Credit: Alex Wild

    Ants are showed for their polymorphism. According to Tulloch (1960), polymorphism is defined as “the condition of having several different forms within a species; as employed by entomologists applies to the coexistence of two or more adult forms of the same sex or caste”.

    First, there are differences between the sexes. The male ant is winged but otherwise markedly different from the winged female of the same species in one or more of the following respects: body smaller and slenderer; colour darker; head smaller; eyes larger; mandibles smaller; antennal scapes shorter; antennal funiculi longer and finer; genitalia more conspicuous.

    The female sex is divided into two castes: queen and worker (neuter). The workers are always wingless and are normally described as sterile. They can, however, on occasion lay eggs. Since workers do not mate, their eggs develop into males.

    The worker caste may be either uniform (except slight variation in size) or it may be differentiated into subcastes (“phase” or “castes”). When the workers of a species form a graded series (many species in Formica ants) the largest are termed major workers (soldiers), the smallest minor workers (minims), while those of intermediate sizes are loosely termed “medias”. The differences between the worker subcastes are not limited to size: the head becomes disproportionately larger as body-size increases, and in some species (notably the rufa-group of Formica ants) the colouration is different.

    The queen look likes the worker more than the male. She is winged before her mating flight and wingless thereafter. The queen is usually larger than her workers; also her thorax and gaster are disproportionately larger and the former bears wing scars.

    The sole function of the male is the insemination of the female; subsequently his life is very short-lived. The functions of the queen are to disperse the species by the mating flight, to found a new colony and become the egg-layer of the new colony. The queen is living up to ten years. All other functions are performed by the workers: nest constructions, defense, food gathering, care of the queen and the brood.
    ( Wheeler and Wheeler, 1963)