Social Insect

We often have heard of the term social insects as they are one of the most dominant and prolific among all the other organisms known to us. One of the most common names that come to mind when we hear the term common insect are ants that work in collaboration and reflect a community structure. Though there are various and numerous varieties of social insects and few mammals as well but major distinguishing factors among the varied social insects are the structures, functioning, behaviour in their casts but the major scale of differentiation is their reproductive patterns where the queen is responsible for the reproduction and the and the steriles who functions as workers and soldiers. The members of the reproductive cast not only carries out reproduction but is also responsible for the selection of the sites to establish their colony and also excavates the first galleries. The workers care for the eggs as well as larva and arrange for the food for the entire colony with building and repairing work of the galleries of the colony whereas the soldiers are responsible for protecting the colony from the attraction of the predators. This article deals with the types and the names of social insects with their characteristics, taxonomy and behaviour pattern.   

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What is a Social Insect?

Many of the insects like bees, ants and many such other animals exhibit social behaviour in terms of feeding aggregation, communal nest sites as well as parental care of the adults for the younger ones. In short, any category of insects where one of the kind interacts with the rest of the members of the same species are considered social in broader terms. But according to the rule set by the emotologists, just a few of these behaviours are not considered enough to be classified as a true social insect or euosocial in nature. Eusociality is considered as the highest level of social culture adopted by eusocial insects that exhibits characteristics like sharing common nest site, cooperative brood care where the individuals of the same species contributes equally in caring for an offspring, overlapping of the generations within the community of adults which means that the youngs contribute to the working force of the community while the adults are still alive and most importantly the division of the labours into productive and non-productive zones, that is, steriles works for the benefits of the productive class of insects in the same community. Thus social insects meaning, any insect that exhibits the above mentioned characteristics in their entire lifespan. Few of the names of social insects are broadly classified as all isoptera, formicidae and hymenoptera. The names of the social insects that fall under the above categories are white ants,ants, bees, wapes and termites where the bees, wasps and ants are of hymenoptera genus and termites are of isoptera genus. In some of the habitats the biomass produced by the ants and termites alone surpasses the biomass produced by all other species combined. Social inset named driver ant found in African Sarvana builds a single colony that comprises approximately close to 20 million workers. Another social insect named Formica Yessensis whose habitat is in Japan where they form a megacolony with almost 45000 interconnecting nests with over a million of queens and more than 405 million of steriles together covering an area of almost 2.7 kilometers.  

Types of Social Insect

Brachycerans are the flies that are mostly associated with the social insects. Among the Brachycerans that are associated with the social insect, Phoridae are known to be the most diverse in nature. These flies are generally associated with army ants both old and old world, termites and lesser known social bees and wasps. Many of them are divided into categories of parasitoids, parasitized and scavengers. The phoridae that lay their eggs in the adult host’s bodies are classified as parasitoids (mostly ants, stingless bees and termites) and they are generally large in numbers whereas parasitizes are the phoridae that are not fully grown into adults. Most of them are scavengers that live in the refuse piles of the large colonies where army ants and leaf cutter ants also reside and they are joined by the larvae of other scavenger ants of the family. Some of the phorid and syrphides larvae are closely similar to that of the ant larvae and thus they are predatory on the ant broots. The adult females of a particular genus of phorids that are mostly found in Southeast Asia have their larvae that mimic the larvae produced by the adult hosts of army ants. The female phoids have a modified structure with reduced wings, eyes and a part of the cuticle of their body whereas the syrphides have a rounded more of a teardrop sized body and are heavily armored so that they can easily escape without much damage to them when aggressively attacked by the army of ants, bees and termites. Thus there has been huge deviations of social insects but has been broadly categorized into five segments based on their degree of sociality in nature.

1. Subsocial Insects: they are a step above the solitary insects who do not build a colony of interconnected sites and do not exhibit social living. But they provide parental support and protection to their offspring, larvae and eggs for a limited period of time. Most of the insects that fall under this category do not prove nests to keep their eggs safe though there are some exceptions. For instance, giant water bugs fall under this category where the female adult bugs lay their eggs on the back of the male bugs who carry the eggs on their back and are responsible for their hatching till they are not hatched.

2. Quasi-Social Insects: they are a little more advanced socially than of subsocial insects. The quasi-social insects share a common nest together with a single generation. They exhibit cooperative parental care for the offspring of the family. A true example of the quasi-social group insect are the orchard bees where the females of a generation share the nest and care and protect their little ones together. But all the bees that share the nest to hatch eggs and cooperatively provide parental care do not necessarily lay their eggs within the nest.

3. Semi Social Insects: semi-social insects are much like the quasi social group in terms of providing parental care, support and protection to their broods in a single nest together that are of the same generation but in addition to it they also have few nonproductive workers. One Of the very common features of semi social insects are the adults takes off as soon as the new generation arrives. The adults leave the nest where the offspring arrives in order to build a new nest or site for the young. The most common example of a semi-social group is paper wapes where the non-productive workers along with the productive group help in expanding and building new nests for the young to grow in.

4. Primitively Eusocial Insects: they exhibit all the characteristics of completely social insects. But the main difference between the eusocial and the primitively eusocial insects are in the structure of the sterile worker casts. In primitive eusocial insects, the insects of all the casts are productive. The scavengers or sterile or army groups are all the same with very minute or absolutely no morphological differences. For example, some of the species of sweat bees are considered primitively eusocial as they show no morphological differences in their cast but bumblebees being considered as primitively eusocial insects, the size of the queen bee is slightly bigger than the size of the sterile casts.

The following table helps us to understand the degree of sociality of the social insects where the bottom groups being the list social to the top with increasing degree of sociality of the species. Thus the social insect list is as follows:-

List of Social Insects

Characteristics of Social Insects

A very common characteristic that is exhibited by almost all the social insects, specially ants and termites is trail pheromones which is generally used to mark feeding or nest sites by leaving trails.  It is a common pheromone of the social insects where the forage on the ground leaves a trail and these characteristics are also shown by some of the sub social species of insects. For example, termites execute the trail pheromone every time their abdomen touches the ground. Everytime their abdominal gland touches the substrates they deposit a drop of their abdomen excrete and forms a well-defined trail as they move around from their nests. The working caste who follows, subsequently works on reinforcing the well laid trail by the initial group of the caste. Even the tent caterpillars over mark their original path taken from the nest to the food supply site by pressing their end of the abdominal part on the ground while returning to their nest from the site of food supply. Even the flying insects follow the chemical trails. For example, the stingless bees belonging to the genus Trigona marks their trail that is usually of citral and they lay down the pheromone while their way back to the nest from the food supply sites. It has been studied that in order to maintain a structural balance of the colony of social insects, trail pheromone is an important characteristic.it helps in regulating many aspects of honeybees. For example, honeybees have been using 36 different forms of pheromone trail using 15 different glands. Pheromones have been involved since the primitive eusocial groups in a diverse behaviours that involve trail marking, colony defence, colony fission, mating, foraging and swarming. Some of the other basic characteristics that the entomologists classified as true eusocial behaviours are as follows:

1. Cooperative parental care of the offspring by the entire family of all generations.

2. Sharing a common nest where the entire colony is established for all the castes of the group of a species.

3.  overlapping of the generations within the community of adults which means that the youngs contribute to the working force of the community while the adults are still alive

4. Division of the working class where the queens are responsible for reproduction whereas the workers are responsible for taking care of the eggs while fetching food as well as building and fixing of sites and the army caste is responsible for the protection and guarding of the colony.

The generation overlapping is very well perceived in termites where there is a constant cycle of the new adults who take the responsibility to take care of the colony and together care and support to bring up the offsprings. In termites, the reproduction caste consists of king and queens who are of the biggest size followed by the army or the soldier caste that comprises both male and female responsible for the protection of the colony from the predators and are larger than the worker class but smaller than the reproduction class and finally comes the worker class that is responsible for the building of the colony and to regulate the food supply with taking care of the eggs in the sites.   

Advantages of the Behaviour of Social Insects

The social insects evolved to be much stronger and competitive for survival as compared to their solidarity counterparts because of the large numbers and the group that lives in the system. As the social insects work together to find food supplies and other day to day commodities and have a characteristic of communicating to the other members of family they acquire a strong defense and execute a vigorous attack in order to defend their homes and other resources when under threat. Because of their community belonging and colonial system they can outcast other animals even bigger and stronger than them for food and territory. They have an ability to quickly build up their colony and expand them according to the need and as the work is divided among various castes thus the work is done in a very systematic way and everything gets done expeditiously. But due to their large numbers the human habitat experiences some disadvantages. For instance, the leafcutter ants found in South America consume more foliage than are consumed by herbivorous mammals and in the southwest United States most of the seeds are collected and eaten up by the harvester ants compared to all the life forms combined.