Centipedes And Millipedes



Dave Rushworth


As children, we used to tell each other that if you squashed a ‘Tjongololo' it would cause it to rain. Even if this is not true, I guess there must have been many run over on the roads during the holiday season - judging by the recent widespread rains. There is little published information available on the subject but I have managed to glean some details from the ‘Encyclopaedia of Insects' - edited by Christopher O'Toole (George Allen & Unwin, London), which I would recommend for further reading.

Your own observations may well add to our existing knowledge of these interesting creatures. Both centipedes and millipedes belong to the super-class Myriapoda - of which they form about 95% - and are creatures that thrive in moist, humid conditions. There are many to be seen in gardens and crossing roads at this time of year. During the dry months they hide away, usually burrowing vertically into the soil to locate suitable moisture and temperature conditions.

They are found from the poles to the tropics, with some millipedes specially adapted to desert conditions. They breathe through ‘spiracles' (holes) along the body which cannot close, as in other members of the phylum Arthropoda. Most species also lack wax in the cuticle of their exoskeleton. These features expose them to desiccation unless they stick to humid conditions or nocturnal activity.

They also lack true compound eyes of insects and have many more legs and no wings. They do not have direct copulatory organs. Centipedes deposit sperm on a pad which is picked up by female. Millipedes deposit the sperm with an adapted pair of legs. The main difference between centipedes and millipedes, apart from their general shape, is that centipedes have one pair of legs per segment while millipedes have two pairs of legs per body segment.

Centipedes

The name means ‘hundred legs'. There are around 3,000 species in the class Chilopoda, which is divided into four different orders. Some species do have up to 177 pairs of short legs but the centipedes most familiar to us belong to the order Scolopendromorpha, which have 21 to 23 pairs of legs - less than half the number their name infers. Centipedes are voracious carnivores, preying on insects, snails and worms, with the largest ones (up to 33cm) able to overpower lizards, frogs and small rodents.

Prey is sensed by the antennae, grabbed with the legs and then stunned using the ‘maxillipeds', which are a modified, pincerlike, pair of legs behind the head. The maxillipeds have sharp, piercing points with a hollow duct leading to a venom gland. They eat with their jaws. Some species have venom that can be extremely painful to humans, although normally of the intensity of a bee sting.

There are no verified reports of human deaths from centipede bites. In the event of disturbance they can produce defensive secretions or toxins in their spiny legs, each from ‘repugnatorial glands'. This may be the cause of inflamed marks on the skin reported by people who have had a centipede walking over them. These secondary infections from centipede claws should be cleaned with disinfectant. Centipedes are extremely useful to farmers and horticulturalists for their destruction of crop pests.

Millipedes

The name means ‘thousand legs' but the maximum number of legs on any species is around 400. There are around 8,000 species in the class Diplopoda (two legs per segment), which is divided into two sub-classes. Sub-class Pselaphognatha consists of one order of small soft-bodied creatures in soil and humus. Sub-class Chilognatha is divided into nine orders which include pill millipedes, flatbacked millipedes and many others.

The millipedes most familiar to us - hard shelled, cylindrical, normally black with brown with yellow or red legs - but sometimes with yellow banded shell - belong to the latter sub-class in the order Julida. Millipedes are herbivores which eat decomposing plant matter in soil and litter. Certain species also eat fine roots and seedlings and can be horticultural pests. Some have developed sucking mouthparts and can suck sap from plants while a few species are predatory.

Generally, they are useful decomposers. Their main defence is the thick cuticle consisting of up to 100 segments. They have open spiracles on the sides of each segment through which they breathe. A few, such as the Polydesmids and Julids, may produce defensive secretions of iodineor cyanide-based droplets or sprays when severely provoked. They are not recorded as being toxic to humans although one can see the yellow stain of iodine on one's fingers after handling some of them.

At boarding school we used to make ‘new boys' swallow them whole during ‘initiation' - and none of them ever suffered from any ill effects. There was a sordid interest in the toilet pans to see whether the creatures had survived their passage through the human alimentary canal but we never discovered any live ones! Under natural conditions, millipedes are preyed on by some birds, such as red-winged starlings and also mammals such as civets, mongooses and hedgehogs.

The exoskeleton remains can usually be found in civet middens and the bleached remains of desiccated individuals can often be found in the veld. Insect predators include larger scorpions and one particular assassin bug (Ectrichodia crux), that looks like one of the large ground beetles and has piercing mouth parts. Location of food items and the opposite sex is conducted through touch by antennae, sound (leg stridulations) and pheromones.

They also have sensory organs in the front and rear leg sections. The area of the fifth to seventh segments have modified pairs of legs that collect sperm and transfer it to the female. Eggs are laid in underground nests sometimes constructed from their own excrement and they moult seasonally in similar dry-season chambers. Desert species produce protective wax and can regulate ‘blood' concentrations for survival.

How do they manage to walk in such an orderly fashion with all those legs to manipulate? The numerous legs are moved in waves at a time. When walking normally they deploy 15 - 20 pairs of legs per wave but when pushing through some object they use 20 - 50 pairs of legs per wave for better traction.

They have a unique method of ‘gear change' - and they have never been known to trip! THINK!! - How is it that these basic creatures manage to control so many legs in an orderly fashion while we humans find it so difficult to control the use of one little tongue and only two hands?



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