Glossary

Head. The head is the first main section of the insect's body. It hosts most of the sensory organs, as well as the initial portion of the digestive tract. The shape the head and its elements vary greatly, depending on the lifestyles of the ant species.

Mesosoma. The mesosoma is the second main section of the ant's body, following the head. Morphologically, it consists of the three thoracic segments (prothorax, mesothorax, and metathorax) and the propodeum, which is connected to the petiolum.

Petiolum. Highly variable in shape, the petiolum connects the mesosoma to the gaster and corresponds to the second abdominal segment. Its shape differs significantly across ant groups, making it a crucial characteristic for identifying ant subfamilies. The petiolum is formed by a tergite and a sternite, which are sometimes fused.

Gaster. The gaster is the largest part of the ant's abdomen and consists of three or four abdominal segments. The terminal portion may exhibit an acidopore (as in Formica paralugubris) or a sting, as well as a variety of glands that emit chemical signals.

Acidopore. An orifice capable of spraying formic acid, characteristic and diagnostic of the subfamily Formicinae (to which Formica paralugubris belongs). It is placed in the terminal end of the gaster. It appears as a short nozzle, typically adorned with a sparse fringe of bristles at its apex.

Sting. A modified and stiffened ovipositor used for penetrating the body of aggressors. This thin needle injects toxic substances from the poison gland (known as Dufour’s gland). However, it is not present in all ants—subfamilies like Formicinae and Dolichoderinae lack a sting.

Femur. The femur is the longest joint in the leg and connects to the coxa, the structure that attaches the limb to the mesosoma.

Tibia. The tibia is the leg segment between the femur and the tarsus.

Tarsus. The tarsus is the final segment of the leg, made up of five sub-segments (called tarsomeres). It plays a crucial role in weight distribution during locomotion.

Tarsal claw. The tarsal claw is the apex of the tarsus, consisting of two curved elements. It may feature a small suction membrane (called an arolium) between them. This membrane helps ants walk on smooth surfaces or upside down, by also providing a secure grip when carrying heavy loads.

Ocelli. Ocelli are simple eyes, typically grouped on the top of the head when present. Unlike compound eyes, ocelli do not produce images, but they help ants in detecting polarized light. This is particularly beneficial for alates during nuptial flights or for workers navigating open, bright environments.

Compound eyes. Compound eyes are capable to produce images, much like human eyes. As in most other insects, these are known as "complex eyes", as they consist of numerous ommatidia—simple photoreceptor units—that collectively form a clearer image of the surrounding environment. In ants, compound eyes vary greatly in size, being very small in hypogeous species and highly developed in species adapted for predation.

Setae. Setae are thick, vertical hairs with a purely sensory function. They play an important role in the identification of different ant species.

Antennae. In ants, the antennae are divided into two main segments: the scape and the funiculus. The funiculus is in turn composed of a variable number of smaller segments, called antennomeres. The right-angle shape formed between the scape and the funiculus is known as geniculata, which is a distinguishing feature of ants compared to other hymenopterans. The mobility of the antennae is facilitated by the antennal condyle (or bulbus), a small spherical structure at the base of the scape. Through their antennae, ants detect chemical signals, such as pheromones, emitted by their nest mates and communicate information in return. For example, rhythmic touches of antennae on the mandibles of a nest mate stimulate trophallaxis.

Clypeus. The clypeus is a thin sclerite that forms the final margin of the head and articulates with the labrum. Its shape is variable, typically trapezoidal or triangular, and it may feature thin crests called carinae in its center. These carinae can give the clypeus a knurled appearance, which is an important feature for accurately identifying different species of ants.

Mandibles. Mandibles are appendages used by ants to grasp various objects, including food, larvae, and structural elements of the nest. Their shape can vary greatly depending on the feeding habits or behaviors of different species. In general, mandibles are composed of two curved, triangular elements that feature a variable number of teeth and denticles on the inner margin. The degree to which mandibles can open also varies significantly among ant species.

Holometabolism. Holometabolism is the most complex developmental cycle in insects. After hatching from the egg, holometabolous species undergo several larval stages, one or more pupal stages (during which metamorphosis occurs), and ultimately reach the adult form. Because of these distinct stages, holometabolism is also referred to as a "complete cycle". Examples of insects that follow this cycle include butterflies, which progress through the caterpillar (larval) stage, the chrysalis (pupal) stage, and finally emerge as adult butterflies. Ants, along with all other hymenoptera, are also holometabolous insects.

Larvae. The larval stage is the first immature stage in holometabolous insects. Upon hatching from the egg, the larva undergoes a series of molts before transforming into a pupa. In ants, larvae are legless (and are thus called apodous larvae) and have a segmented, bristled body, typically divided into 13 segments. The development of larvae into workers rather than queens can be influenced by nutritional, environmental, or hormonal factors.

Pupae. The pupal stage occurs between the larval and adult (also called imago) stages in holometabolous insects. In some ant species, such as Formica paralugubris and others in the rufa group, the pupa is encased in a cocoon. In other species, the pupa remains exposed. During this stage, the insect cannot feed and relies on energy stored during the larval stage to undergo metamorphosis and develop into its adult form.

Imago. The imago is the adult stage of an insect, marking the final phase of its development.