The superorder Acariformes represents one of the two primary lineages of mites, showcasing an extraordinary level of diversity and abundance. These microscopic arachnids have successfully colonized nearly every conceivable habitat on the planet. With an estimated one million species, many of which are yet to be discovered, they constitute a significant portion of arthropod biodiversity. Their presence spans from the deepest soils to the highest canopies, and from freshwater springs to oceanic trenches.
Defining Biological Characteristics
Acariformes are unified by a distinct set of anatomical features, chief among them being their body plan. The body is divided into two main regions: the gnathosoma and the idiosoma. The gnathosoma contains the mite’s mouthparts, which are adapted for a wide variety of feeding methods, while the idiosoma comprises the rest of the body, including the legs and internal organs.
A feature used to distinguish Acariformes from the other major mite superorder, the Parasitiformes, relates to their respiratory system. Most Acariformes lack stigmata, or breathing pores, located near the base of their chelicerae (mouthparts). Instead, respiration often occurs directly through the cuticle or via a tracheal system with openings located elsewhere on the body.
The life cycle of an Acariforme mite progresses through several distinct stages. Development begins with an egg, which hatches into a prelarva, a non-feeding, immobile stage. This is followed by the larval stage, which is characterized by having only three pairs of legs. The larva then molts through a series of nymphal stages—commonly a protonymph, deutonymph, and tritonymph—each progressively larger and more developed, before finally reaching the sexually mature adult stage.
Ecological Diversity and Lifestyles
The ecological range of Acariformes is vast, as they are found in terrestrial, freshwater, and even marine environments, occupying a multitude of niches within these ecosystems. In terrestrial systems, they are particularly abundant in soil and leaf litter, where some groups can reach densities of thousands of individuals per square meter. Their ability to thrive in such varied conditions is a result of their diverse lifestyles and feeding habits.
Feeding strategies among Acariformes are incredibly varied. Many species are detritivores, playing a role in the decomposition of organic matter and nutrient cycling in soil ecosystems. Others are herbivores, feeding on a wide range of plants, from algae and fungi to higher plants. Predatory species are also common, hunting other small arthropods, nematodes, and their eggs.
A significant number of Acariformes have adopted parasitic lifestyles, living on or within other organisms. These parasitic relationships span a wide spectrum of hosts, including both invertebrates and vertebrates. Plant-parasitic mites can be found on virtually all types of plants, while animal parasites have adapted to live on mammals, birds, and other animals.
Major Subgroups and Common Examples
The superorder Acariformes is divided into two principal lineages: the Sarcoptiformes and the Trombidiformes. The Sarcoptiformes are a diverse group that includes many free-living decomposers as well as a number of well-known parasitic species. They are often characterized by their slow-moving nature and robust bodies.
Within the Sarcoptiformes, some of the most recognized examples are those that directly interact with humans. Dust mites, such as Dermatophagoides pteronyssinus, are a familiar example, thriving in human dwellings and feeding on shed skin cells. Another prominent member is the scabies mite, Sarcoptes scabiei, a parasitic mite that burrows into the skin of humans and other mammals, causing the infectious skin condition known as scabies.
The Trombidiformes represent an even more diverse and species-rich lineage, encompassing a vast array of forms and lifestyles. This group includes predators, plant feeders, and parasites. Their diversity is reflected in their morphology, with a wide range of body shapes, colors, and sizes, from microscopic to several millimeters in length.
Well-known examples from the Trombidiformes include several mites of economic and medical importance. The Tetranychidae family, commonly known as spider mites, are agricultural pests that feed on hundreds of species of plants. Larvae of the Trombiculidae family are known as chiggers, which can deliver itchy and irritating bites to humans and other vertebrates. The large, brightly colored velvet mites of the Trombidiidae family are predators, feeding on other small arthropods and their eggs.
Impact on Human Health and Agriculture
The activities of Acariformes have direct and significant consequences for human health. Certain species are responsible for causing allergies and diseases in humans and domestic animals. Dust mites, for instance, are a primary source of indoor allergens, with their waste products triggering allergic rhinitis and asthma in susceptible individuals. The scabies mite causes a contagious and intensely itchy skin infestation that requires medical treatment to resolve.
In the agricultural sector, various Acariformes species are considered major pests. Spider mites are among the most destructive, feeding on a wide variety of crops, including fruits, vegetables, and ornamental plants. Their feeding can reduce plant vigor, decrease yields, and in severe cases, lead to plant death.
Despite the negative impacts of some species, many Acariformes play beneficial roles. As decomposers in soil ecosystems, they are instrumental in breaking down dead organic material and recycling nutrients, which is fundamental to maintaining soil fertility. Furthermore, some predatory mites are used as biological control agents in agriculture, where they are released to prey on and control populations of pest mites and insects.