Millipede facts for kids
Quick facts for kids Millipedes |
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Diplopoda
de Blainville in Gervais, 1844
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Helminthomorpha |
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Millipedes are a group of arthropods. They have two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda. Most millipedes have very elongated round or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball.
There are approximately 12,000 named species classified into 16 orders and around 140 families, making Diplopoda the largest class of myriapods. Most millipedes eat decaying leaves and other dead plant matter. Some eat fungi or suck plant fluids, and a small minority are predatory.
Millipedes are generally harmless to humans, although some can become household or garden pests causing severe damage to emergent seedlings. Most millipedes defend themselves with a variety of chemicals released from pores along the body, although the tiny bristle millipedes are covered with tufts of detachable bristles.
Contents
Evolution
Millipedes are among the first animals to have colonised land during the Silurian period. Early forms probably ate mosses and primitive vascular plants. There are two major groups of millipedes whose members are all extinct: the Archipolypoda ("ancient, many-legged ones") which contain the oldest known terrestrial animals, and Arthropleuridea, which contain the largest known land invertebrates.
The earliest known land creature, Pneumodesmus newmani, was a 1 cm (0.4 in) long archipolypodan that lived 428 million years ago in the upper Silurian, and has clear evidence of spiracles (breathing holes) making clear evidence of its air-breathing habits. Arthropleura became the largest known land-dwelling invertebrate on record, reaching lengths of at least 2 m (6 ft 7 in). Millipedes also exhibit the earliest evidence of chemical defence.
Distinction from centipedes
The differences between millipedes and centipedes is a common question from the general public. Both groups of myriapods share similarities, such as long, multi-segmented bodies, many legs, a single pair of antennae, and the presence of postanntennal organs, but have many differences and distinct evolutionary histories. The head alone demonstrates the differences; millipedes have short, elbowed antennae for probing, a pair of powerful mandibles and a single pair of maxillae (paired structures present on the head as mouth-parts) fused into a lip; centipedes have long, threadlike antennae, a pair of small mandibles, two pairs of maxillae and a pair of large poison claws.
Distinction from pill bugs
Oniscomorpha is a superorder of millipedes that are commonly called pill millipedes due to their resemblance to certain woodlice (Oniscidea), also called pill bugs or "roly-polies". However, millipedes and woodlice are not closely related; rather, this is a case of developing similar visual traits in the same environment, during evolution.
Characteristics
Millipedes come in a variety of body shapes and sizes, ranging from 2 mm (1⁄16 in) to around 35 cm (14 in) in length, and can have as few as eleven to over three hundred segments. They are generally black or brown in colour, although there are a few brightly coloured species, and some have aposematic colouring to warn that they are toxic.
Body styles vary greatly between major millipede groups.
Head
The head of a millipede is typically rounded above and flattened below and bears a pair of large mandibles. The head contains a single pair of antennae with seven or eight segments and a group of sensory cones at the tip.
Millipede eyes consist of several simple flat-lensed ocelli arranged in a group or patch on each side of the head. These patches are also called ocular fields or ocellaria. Many species of millipedes had ancestors that could see but have subsequently lost their eyes and are blind.
Body
Millipede bodies may be flattened or cylindrical. They are composed of numerous metameric segments, each with an exoskeleton.
The first segment behind the head is legless and known as a collum (from the Latin for neck or collar). The second, third, and fourth body segments bear a single pair of legs each and are known as "haplosegments" (the three haplosegments are sometimes referred to as a "thorax"). The remaining segments, from the fifth to the posterior, are properly known as diplosegments or double segments. Each diplosegment bears two pairs of legs, rather than just one as in centipedes. In some millipedes, the last few segments may be legless. The terms "segment" or "body ring" are often used interchangeably to refer to both haplo- and diplosegments. The final segment is known as the telson and consists of a legless preanal ring, a pair of anal valves (closeable plates around the anus), and a small scale below the anus.
Millipedes in several orders have keel-like extensions of the body-wall known as paranota, which can vary widely in shape, size, and texture; modifications include lobes, papillae, ridges, crests, spines and notches. Paranota may allow millipedes to wedge more securely into crevices, protect the legs, or make the millipede more difficult for predators to swallow.
The legs are composed of seven segments, and attach on the underside of the body.
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Internal organs
Millipedes breathe through two pairs of spiracles located ventrally on each segment near the base of the legs. Each opens into an internal pouch, and connects to a system of tracheae. The heart runs the entire length of the body, with an aorta stretching into the head. The excretory organs are two pairs of malpighian tubules, located near the mid-part of the gut. The digestive tract is a simple tube with two pairs of salivary glands to help digest the food.
Reproduction and growth
In the basal order Polyxenida (bristle millipedes), mating is indirect: males deposit spermatophores onto webs they secrete with special glands, and the spermatophores are subsequently picked up by females. In all other millipede groups, males possess one or two pairs of modified legs called gonopods which are used to transfer sperm to the female.
Females lay from ten to three hundred eggs at a time, depending on species. Many species deposit the eggs on moist soil or organic detritus, but some construct nests lined with dried faeces, and may protect the eggs within silk cocoons. In most species, the female abandons the eggs after they are laid, but some species in the orders Platydesmida and Stemmiulida provide parental care for eggs and young.
The young hatch after a few weeks. They typically have only three pairs of legs, followed by up to four legless segments. As they grow, they continually moult, adding further segments and legs as they do so. The adult stage, when individuals become reproductively mature, is generally reached in the final moult stage.
Habitat and distribution
Typically forest floor dwellers, millipedes live in leaf litter, dead wood, or soil, with a preference for humid conditions. Some species can survive freshwater floods and live submerged underwater for up to 11 months. A few species occur near the seashore and can survive in somewhat salty conditions.
Interactions with humans
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Millipedes do not bite, and are mostly harmless to humans. However, the secretions of some tropical species may cause pain, itching, local erythema, edema, blisters, eczema, and occasionally cracked skin.
Eye exposures to these secretions causes general irritation and potentially more severe effects. This is called millipede burn. First aid consists of flushing the area thoroughly with water; further treatment is aimed at relieving the local effects.
Some millipedes are considered household pests. They can cause significant damage to crops: the spotted snake millipede is a noted pest of sugar beets and other root crops. Some of the larger millipedes are popular as pets.
Interesting facts about millipedes
- The name "millipede" comes from the Latin for "thousand feet."
- Despite the common name, no millipede was known to have 1,000 legs until 2021: the record is held by Eumillipes persephone, with individuals possessing up to 1,306 legs – more than any other creature on Earth.
- Approximately 12,000 millipede species have been described. Estimates of the true number of species on earth range from 15,000 to as high as 80,000.
- Millipedes occur on all continents except Antarctica.
- They may live from one to ten years, depending on species.
- Millipedes are susceptible to water loss and with a few exceptions must spend most of their time in moist or humid environments.
- In 1963, a walking vehicle with 36 legs was designed, said to have been inspired by a study of millipede locomotion.
Images for kids
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Approximate relative diversity of extant millipede orders, ranging from ca. 3,500 species of Polydesmida to 2 species of Siphoniulida
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Octoglena sierra (Colobognatha, Polyzoniida)
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Anadenobolus monilicornis (Juliformia, Spirobolida)
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Harpaphe haydeniana (Polydesmida)
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Pauropods are thought to be the closest relative of millipedes.
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A Sceliages beetle transporting a millipede carcass
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Ammodesmus nimba from Guinea, West Africa, curled in a defensive coil
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Flat millipede found in the Mount Cameroon Forest
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See also
In Spanish: Milpiés para niños
