| Differences between Centipedes (Chilopoda) and Millipedes (Diplopoda) | |
| Centipedes | Millipedes |
| one pair or two legs on each segment; adult leg no. ranges from 30 (15 pairs) to 382 (191 pairs) on Gonibregmatus plurimipes Chamberlin in the Fiji Islands (Geophilomorpha: Gonibregmatidae). | two pairs or four legs on most segments because these are really "diplosegments" formed by fusion of adjacent somites in the embryo; legs always on metazonite, representing caudal of fused somites; adult leg no. ranges from 22 (11 pairs) to 750 (375 pairs) on Illacme plenipes Cook and Loomis in San Benito Co., CA (Siphonophorida: Siphonorhinidae). |
| legs extend laterad and are clearly visible on sides of body; this position provides little support and the body is carried low to substrate. | legs extend at most only slightly laterad and are only partly visible on sides of body; this position provides strong support, and the body is carried high off substrate. |
| last legs extend backwards behind the body and are not used for locomotion. | last legs extend sideways parallel to other legs. |
| legs articulate laterally with body. | legs articulate mid-ventrally with body; as the legs provide the pushing/burrowing power, this position allows for longest possible legs and greatest power with least lateral extension, minimizing chance that legs might be broken in narrow spaces that millipedes inhabit. |
| flexible, dorsoventrally flattened arthropods (except Scutigeromorpha, which is not flattened). | relatively inflexible arthropods with variable body forms that, in general, are subcylindrical. |
| almost exclusively carnivores. | primarily detritivores, though carnivory occurs occasionally in a few species; most species in subterclass Colobognatha have long, narrow, "sucking" mouthparts, food source and method of feeding unknown; millipedes are ecologically important in fragmentation of leaf litter, which facilitates microbial decomposition and soil nutrient cycles. |
| adapted for speed (except for Geophilomorpha, which moves slowly and burrows). | primarily slow moving arthropods adapted for burrowing and 3 dfferent burrowing mechanisms are known; some species have lost this ability and are surface active, while others are too thin and weak to burrow and inhabit existing cracks and crevices. |
| adults vary in length from 10-270+mm (1/2-10 ½ in.); largest sp. is Scolopendra gigantea L. in northern South America; largest North American sp. is S. heros Girard from AR/MO to AZ and northern Mexico (ca. 153 mm, 6 in). | adults vary in length from 3-270+mm; longest sp. is Archispirostreptus gigas (Peters) in Africa; longest North American sp. is Paeromopus paniculus Shelley and Bauer in CA (Yosemite Nat. Pk. & vic.) (160 mm, 6 ½ in.). |
| have prehensors ("poison claws") under head with which they kill prey, and large species can inflict a painful bite on man (only one suspected death from centipede bite, a small child in Philippines bitten on head); these are actually modified legs and appendages of the first segment; they are not mouthparts and aren't associated with the head. | lack structures to bite, pinch, or sting, and are harmless to man, although defensive secretions burn if get into eyes; a few large species in neotropics can squirt defensive secretions a couple of feet and have blinded chickens and dogs. |
| occur in all habitats and are prominent in deserts and arid environments. | occur primarily in moist deciduous forests because most species lack a waxy cuticle as a dessication barrier; some species occur at high elevations in "alpine" environments and a few thrive in deserts. |
| spiracles located laterally (middorsally in Scutigeromorpha); in some forms they are valvular and can be closed. | spiracles located ventrally; they are never valvular and cannot be closed. |
| "opisthogoneate"; reproductive tracts open at caudal end of body. | "progoneate"; reproductive tracts open near anterior end of body, specifically on segment 3; in most millipedes (infraclass Helminthomorpha) copulatory structures in males located caudal to seg. 3, either on seg. 7 or segs. 7 & 8. |
| males do not possess modified legs for reproduction. | in subclass Chilognatha, males possess modified legs; in infraclass Pentazonia these involve 1-(?)3 pairs of legs at caudal end called "telopods" that function either to clasp female during reproduction or deposit spermatophore directly in female openings; in infraclass Helminthomorpha insertion is accomplished by "gonopods" on segment 7; depending upon order either anterior leg pair on seg. 7, or both pairs on seg. 7, or posterior pair on seg. 7 and anterior pair on seg. 8 are so modified. |
| primarily use prehensors for defense; also employ aposematic coloration, luminescence, and some species, especially scutigeromorphs, can autotomize legs; some species produce defensive secretions. | primarily employ defensive secretions from segmental defensive glands that open laterally (middorsally in one family) [not all families have defensive glands]; secretions contain variety of noxious chemicals (quinones, terpenoid compounds, etc.) and one order, Polydesmida, produces cyanide; also employ defensive posture of coiling into protective spiral and in some orders a perfect ball or sphere with head in center; also employ aposematic coloration to warn of toxic defensive secretions and species of genus Motyxia in southern California are bioluminescent. |