Myriapods represent a diverse and ancient group of arthropods, often recognized by their numerous legs. These fascinating invertebrates are terrestrial organisms, with over 13,000 known species inhabiting various environments worldwide. Myriapods have a long evolutionary history, with fossil records dating back to the Late Silurian and Early Devonian periods, highlighting their enduring presence on Earth. Despite their widespread distribution, myriapods are frequently misunderstood, often due to their secretive nature and preference for hidden habitats.
Defining Myriapods
Myriapods are characterized by their elongated, segmented bodies, divided into two main sections: a head and a trunk. Each segment of the trunk bears one or two pairs of legs, giving them their “many-footed” distinction. A single pair of antennae protrudes from their head, which they use for sensory perception.
Unlike insects, which possess three distinct body segments (head, thorax, and abdomen) and six legs, myriapods have a simpler body plan with many repeating segments. Myriapods also differ from arachnids, which have eight legs and two body segments (a fused cephalothorax and abdomen), and lack antennae. Respiration in myriapods occurs through a tracheal system, a network of tubes delivering oxygen directly to tissues, similar to insects.
The Major Myriapod Groups
The subphylum Myriapoda encompasses four main classes: Chilopoda (centipedes), Diplopoda (millipedes), Pauropoda, and Symphyla.
Chilopoda (Centipedes)
Centipedes have flattened bodies and a single pair of legs on most body segments. They are swift, active predators with venomous fangs, called forcipules. These modified front legs inject venom to immobilize prey. Centipedes feed on insects and other small invertebrates, though larger tropical species can subdue small vertebrates like mice, frogs, or snakes.
Diplopoda (Millipedes)
Millipedes have cylindrical bodies with two pairs of legs on most segments. This appearance of double legs per segment arises from the fusion of two embryonic segments into one. Millipedes are slow-moving detritivores, feeding on decaying plant matter such as leaf litter and organic debris. When threatened, many millipedes coil into a tight spiral or ball to protect their vulnerable undersides. They also secrete noxious or poisonous chemicals, sometimes containing cyanide, through pores on their sides for defense.
Pauropoda
Pauropods are tiny myriapods, measuring between 0.5 to 2.0 millimeters in length. They are pale, soft-bodied creatures that lack eyes, relying on their branched antennae and vibration-sensitive organs (pseudoculi) for navigation. Pauropods have 9 to 11 pairs of legs as adults and prefer moist soil environments, often found under rocks, wood, or moss. Their diet is not fully understood, but some species consume mold or suck fluids from fungal root-like structures.
Symphyla
Symphylans, sometimes called garden centipedes or pseudocentipedes, are small, white, and translucent myriapods. They range from 2 to 8 millimeters in length, though some species can reach up to 30 millimeters. Symphylans have 11 or 12 pairs of legs and lack eyes, similar to pauropods. They are found in the upper layers of soil and leaf litter, often migrating deeper to escape dry or cold conditions. Many symphylans are omnivores, feeding on fungal hyphae and fresh root material, with some species being saprophagous (feeding on decaying organic matter).
Habitat, Diet, and Behavior
Myriapods are terrestrial arthropods that thrive in moist, dark environments. Their preferred habitats include leaf litter, decaying logs, under rocks, and within soil, where they can avoid desiccation. Their bodies, adapted for these niches, often have thick cuticles to help retain moisture, and their simple eyes or lack of vision mean they rely heavily on their antennae and other sensory organs for navigation.
The dietary habits of myriapods vary between groups. Centipedes are active nocturnal predators, using their speed and venom to capture a wide range of prey, including insects, spiders, and even small vertebrates. Millipedes, on the other hand, are detritivores, consuming decaying plant matter and contributing to the breakdown of organic material in their ecosystems. When disturbed, centipedes flee quickly or may attempt to bite, while millipedes often curl into a protective coil and can release defensive secretions.
Myriapods and Their Ecological Role
Myriapods play significant, though often overlooked, roles in terrestrial ecosystems. Millipedes are particularly important as decomposers, breaking down dead plant and animal matter. This process releases nutrients back into the soil, enriching it and making those nutrients available for plants, thus supporting overall ecosystem health and nutrient cycling.
Centipedes contribute to ecosystem balance as predators. They help control populations of other invertebrates, including insects and spiders, which can impact agricultural and natural environments. While some larger centipede species can inflict a painful bite, they are generally not aggressive towards humans and their venom is rarely life-threatening. Millipedes are largely harmless to humans, though some species can secrete irritating chemicals that may cause temporary skin discoloration or mild burning if handled.