CHILOPODA | Centipedes

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Centipedes have elongated, multi-segmented bodies with fifteen or more pairs of legs when fully developed. They can have many more, but they're always an odd number. Each body segment bears a pair of legs, unlike millipedes that are characterised by having two pairs on most segments. With the exception of the soil centipedes whose legs are adapted for burrowing, the surface-dwelling species possess long legs with each pair being slightly longer than the those in front so they don't overlap when running. Most species are nocturnal, staying hidden away in dark places during the day and coming out at night to feed so, if disturbed and subjected to sunlight, the natural reaction is to quickly run for cover, which they manage to do very efficiently! They are predatory animals that feed on a wide range of small soil-dwelling species including springtails, small spiders and beetles. The foremost pair of limbs extend forward under the head and are modified into claws that include venom glands for paralysing and killing prey. They are known as 'forcipules' and are a unique feeding aid only associated with centipedes. The actual mouthparts consist of a pair of mandibles for cutting, and two pairs of maxillae used for tasting and manipulating food items. Their antennae are typically long and thin consisting of a varying number of parts that, for these species, are called articles rather than segments. Some species are blind, whilst others have ocelli on either side of the head, which are simple eyes not comparable to the compound eyes of insects.

Centipedes go through a series of instars after hatching with some species, notably the geophilomorphs and Cryptops, having the same number of legs as the adults throughout the development process, whereas others will initially have fewer pairs than they will eventually end up with. To complicate matters further they also go through a post-larval stage where they continue to grow with no definitive way of distinguishing whether an individual is immature or a fully developed adult. Some genera include species of varying size where an adult of one species can be smaller than an immature of another. This fact, together with the requirement to examine very small details, means that positive identification of many species is impossible from photos and, as such, specimens are required for close examination. Given that I have no desire to kill a creature just to confirm a name it is inevitable that some of the representative photos of species featured here are, in some cases, 'likely' rather than certain.

There are around 60 species on the British List but, when you start analysing them, you quickly find that many are either non-native or rare and localised. I have around twenty on my 'target list', but would be surprised if I managed to find and photograph more than a dozen or so. They are separated into four distinct orders, GEOPHILOMORPHA (soil centipedes), SCOLOPENDROMORPHA (commonly referred to overseas as tropical centipedes), LITHOBIOMORPHA (stone centipedes) and SCUTIGEROMORPHA (house centipedes), which effectively is a single species that's very unlikely to be encountered. Although they all have a common basic structure, there are certain features that vary from one group or family to another and, therefore, each order needs to be looked at independently.

GEOPHILOMORPHA

MYRIAPODA > CHILOPODA (centipedes) > GEOPHILOMORPHA (soil centipedes)

This large order accounts for just over half the species of centipede that have been recorded in Britain. There are actually 31 on the official list, although only 25 or so of these are normally considered and, of those, many are rare or only occur in particular parts of the country. Obviously, this greatly reduces the number of species that can be found in any given area, and that is certainly true of my local patch where I have only been able to identify ten that could realistically be encountered based on available distribution data.

Geophilomorphs are the so-called soil or earth centipedes that have slender, elongate bodies and numerous short legs adapted for burrowing. They vary in size from as little as 12mm to as much as 70mm with a corresponding number of body segments and legs to match their length. Even the smallest species have a minimum of 35 pairs of legs, but the average number is more like 43-85 pairs, although one particular rare species, Stigmatogaster souletina, actually has 93-101 pairs. The approximate length of the individual together with an accurate count of the number of legs is the starting point for identification and if the sex can be determined it narrows down the options slightly as females typically have a couple of extra pairs. This doesn't always require close examination of their rear ends as there's sexual dimorphism in a number of these species where the last trailing legs of the males are noticeably swollen. Fortunately, the number of leg-bearing segments does not change during the life of a geophilomorph, which means that you're not having to worry about immatures.

The identification 'key' for these particular species also provide some really good comparative data that can be used when checking photos. These include the respective length of the body compared with its thickness, a similar ratio for the length of the antennae compared with the breadth of the head, and other visual features such as the shape of the head and forcipular segment. Obviously, the colour of the species helps, although the paler, whitish and yellowish forms, can be quite variable, but the Strigamia species and Geophilus easoni can be separated from the others as they are clearly darker with a more consistent reddish-brown colour.

These species spend most of their lives in the dark hidden away under stones or beneath deadwood where they can often be found burrowing in the soil or winding themselves into tiny cervices for which their body is well designed. They are eyeless and blind and, as such, are generally slower to react than the Cryptops or Lithobius species when disturbed. That doesn't mean they're easy to photograph though, as you really need to get shots of them on the move rather than curled up where you won't be able to accurately count the legs.

Although many of the important characters such as specific details regarding the legs and/or structures on the trunk sternites are only likely to be discernable with close inspection rather than from photos, I believe that, with the species I'm likely to see locally, the general shape and colour, together with number of legs, and the body and antennae ratios, should provide sufficient information.

To date, I've found eight species in this order, six of which can be confirmed but, typically with similar species, there's always one that has to be officially classed as 'likely' rather than definite.

Stigmatogaster subterranea

Strigimia crassipes

Strigimia acuminata

Geophilus cf.osquidatum

Geophilus easoni

Geophilus truncorum

Geophilus flavus

Schendyla nemorensis

SCOLOPENDROMORPHA

MYRIAPODA > CHILOPODA (centipedes) > SCOLOPENDROMORPHA ('tropical centipedes')

Whilst the current British List includes six species in this small order, only three need to be considered; Cryptops hortensis, and two larger, non-native, but now naturalised species, Cryptops anomalans and Cryptops parisi.

Of these, only Cryptops anomalans can be reliably identified from photos and only then if there's a detailed dorsal view of the first tergite showing a characteristic cruciform suture. It is the largest Cryptops species found in Britain, with some individuals achieving a body length of up to 50mm. To date, it has never been officially recorded either from Dorset or surrounding areas, but that certainly doesn't mean that they're not present.

That leaves Cryptops hortensis and Cryptops parisi and, although, the former is the smaller of the two, always under 30mm when fully developed, size can't be relied on as it's not possible to distinguish between immatures and adults. Yet, even though Cryptops parisi grows to more than 30mm, detailed examination is required for formal recognition. I suspect this is the reason why there are so few records for any of these species. In fact, at the time of writing, there were only 555 records in total; 445 for hortensis, but with only one in Dorset; 84 for parisi where there were none in Dorset; and just 26 nationwide for anomalans, which is ridiculous.

Notwithstanding the above comments, I think that from a personal point of view it's safe to say that as long as Cryptops anomalans has been ruled out, Cryptops hortensis is the most likely species, unless the individual is clearly over 30mm long when, in theory at least, it should be Cryptops parisi.

Cryptops species are typically orange to reddish-brown in colour, and can be recognised by having a circular to oval head with antennae normally composed of 17 articles, although sometimes less, coupled with a body comprising 21 trunk segments, each bearing a pair of legs that gradually increase in size towards the rear with the final pair being markedly larger than the others. Unfortunately, these trailing legs, that are used to help the centipede move backwards out of tight spaces rather than walking, have a tendency to break off, so it's not unusual to find an individual who's lost one or even both! They are fast moving creatures that, in most cases, scurry away rather quickly if disturbed making them particularly difficult to photograph in their natural habitat. It amazes me that they can react so quickly as these species do not have any ocelli, so are effectively blind as they're not even able to detect light and dark in the same way that other species can. Instead, they rely on other faculties including sensory hairs on their antennae that guide their way.

All three species have a strong association with synanthropic sites, particularly Cryptops anomalans, although both Cryptops hortensis and Cryptops parisi have also been recorded from woodland.

Cryptops cf.hortensis

Cryptops sp.

LITHOBIOMORPHA

MYRIAPODA > CHILOPODA (centipedes) > LITHOBIOMORPHA (stone centipedes)

The British List shows 22 species in this order separated into just two genera, Lithobius and Lamyctes. Six of these species are either non-native or of unknown status, and a further nine are scarce, rare or not recorded locally. That leaves just seven species that realistically might be encountered in my general area, six Lithobius spp. and Lamyctes emaginatus.

Unlike the previously featured geophilomorph and Cryptops species that are born with all their legs, these centipedes hatch with a reduced number and go through a series of larval stages during which further legs are added as they grow and then, after the full compliment of 15 pairs are present, they pass through post-larval stages as their bodies continue the development process. Adult lithobiomorphs vary in size from around 10mm to 30mm for the species I'm likely to find, so it can't be assumed that a small individual is immature. However, given that all species have 15 pairs of legs when fully mature, the size is going to be an important identification aid, so obtaining a good idea of the length of an individual is advisable. It's not easy and sometimes almost impossible, but I'm now carrying a small white ruler with me so that I can try to get a measurement or, better still, a photo of it laid alongside the centipede.

Fortunately, there are a few visual characters and features that can be used in conjunction with the size. The most important is the number of antennal articles that differ from one species to another and, although they can also vary a fair bit for any individual species, and overlap between species, an accurate count will help considerably in narrowing down the options. It also helps if you've identified the various species that are likely to be seen, as I have done. Identification keys exist and although some of the important features are only going to be seen with close inspection others, such as whether the tergites have projections, are going to be visible in photos if they show good detail from different angles.

A characteristic of these species is the consistency in body form, in that they all have fifteen trunk segments in both sexes and that these segments consist of mainly alternate large and short tergites along the back. The first large segment behind the head is T1 then T3 and T5, separated by slim segments T2 and T4. There are then two large segments together, T7 and T8, followed by two further large segments T10 and T12, separated by two smaller ones, T9 and T11, and then at the rear T13 and T14. The posterior angles of T7, T9, T11 and T13 may be rounded or angled or may project. The different species vary in colour from light to dark brown, or almost black in the case of Lithobius calcaratus, but with many simply described as chestnut-brown.

I mentioned that there were six Lithobius species that could be found locally and, I believe, to date I've seen three of these.

Lithobius microps

Lithobius forticatus

Lithobius melanops

Lithobius variegatus

Unidentified young Lithobiids

Original list created Oct.22 | updated Jan.24 (v.3)