The Antlion is a voracious insectoid creature of several differing castes, with a hierarchy very similar to that of ants. They are native to Xen.
Antlions are social creatures which live in large underground colonies. They include several castes, such as the Antlion Soldier, which is the most commonly found, the Antlion Worker, which works in nests and protects the Antlion Grubs, the larvaes, the Antlion Guard, a taller Antlion, and the Antlion Guardian, which rules the nests. Antlions are blind and use pheromones and vibrations to identify other living beings.
Antlions were once farmed by Vortigaunts for their larval extract and a number of other purposes; Antlion husbandry was once their ancestral practice.
Their young begin life as larvae in blue honeycombs similar to those of bees. The extract of these larvae is highly prized by the Vortigaunts for its ability to "divide the false veils of the vortessence" when imbibed. This seems to augment their natural powers. The larvae grow into large grubs, which are attended to and protected by Antlion Workers and Antlion Guardians. Within this system, common Antlions presumably serve as hunter gatherers. Inside their nests, decomposed bodies of other creatures can often be discovered, trapped in the viscous silk the grubs produce as a food source, and some of their deepest chambers are pooled with blood.
Since the Combine invasion of Earth and the beginning of the Portal Storms the Antlions have established themselves on Earth. They have obviously been very successful in doing so, possibly to the point of causing extinction to other kinds of Earth fauna. So widespread were the Antlions on Earth that the Combine had to install a large network of thumpers (a large device that pounded the ground, frightening off Antlions) to protect themselves from the creatures. When these were shut down, Combine territories were quickly overrun by Antlions, with chaotic results.
Common Antlions are the most visible element of a larger Antlion society, most of which is kept hidden in fiercely defended underground nests. It is not clear how Antlions breed, although there seems to be a spawning season; whether Antlions mate separately, have a queen/drone system or practice something completely alien to Earth sensibilities is not known.
The Grubs are larvae-like creatures, emitting a high chirping call and bioluminescence similar to that of a firefly. They are found only deep inside Antlion colonies, and can be seen hanging on any available surfaces, often in groups of two or more. They are extremely fragile and can be killed by merely bumping into them. In the hive, human remains are sometimes found scattered on the ground near Grubs, suggesting that they are carnivorous and are presumably provided with food by mature Antlions. Grubs also exude a filmy thread, similar to that of a silkworm but on a much larger scale. Grubs also contain a yellow substance with healing properties. Every Antlion in the nest will protect grubs fiercely.
The Antlion Soldier is a four legged creature around 3 to 5 feet in height and 6 feet from head to tail. Their legs are arranged oddly, with their back legs set at their front, and vice versa. Their hard shells are mostly green with stripes of tan, yellow, purple and red. They have no visible eyes, and have three mouthparts arranged in a triangle on their face. Hidden beneath the Antlions' shells are wings which allow it to fly several feet in the air, making a loud buzzing noise as they take to the air. They are also quite powerful burrowers, able to tunnel through solid rock and even concrete. Antlion Soldiers are charged with gathering food for their nests, using their keen senses of touch and smell to track their prey. Once they pinpoint a potential meal, they swarm the target relentlessly, biting and headbutting their prey until dead, after which they return to their nests with their kill to feed their hungry brood.
Workers are similar to Soldiers in appearnce, although paler and lacking a carapace. Like regular Antlions, workers can fly short distances; however, their wings are smaller, therefore workers cannot fly as far as regular Antlions. Workers primarily attack by hurling 'spitballs' of neurotoxin at foes from a distance with great accuracy, similar to Bullsquids. If caught up close they will attack with their claws, but they usually prefer to use their more powerful ranged attack and will often retreat if their attacker gets too close. These factors combine to make the Antlion worker an uncommonly standoffish foe. When killed, Workers explode in a shower of acid, inflicting considerable splash damage on anything within range.
Guards, also called Myrmidonts by Vortigaunts, are much larger and stronger than Soldiers. Within Antlion society, the Guards defend the Antlion nests' outer perimeter and entrances, and they control and keep order within the Antlion colony. Guards resemble a considerably larger and more powerful Antlion, with a similar skin color and insectoid features. The most differentiating feature, by far, is the Guard's protected carapace, which acts as both a battering ram and a deadly weapon. Their dark-red tint and radiant blue "feathers" which adorn its back make it clearly distinguishable.
It is notable that the Guardian is very similar to the Guard, both in name and appearance, but there are numerous differences: the Guardian often lives deeper within the nests, protecting and ruling over the Antlions and eggs within. Comparatively, the Guard will work nearer to the surface, protecting nest entrances and offering backup for Workers. Also notable is the Guardian's natural bio-luminescence, which is presumably caused by it living in deeper darkness. The Guard also has a very different coloration, consisting of more varied and contrasting colors.