JUMPING BRISTLETAILS (ARCHEOGNATHA) OF BRITISH COLUMBIA
R. A. Cannings and G. G. E. Scudder
Copyright © 2005 - All rights reserved
Extracted from the forthcoming publication The Insect Families of British Columbia
Introduction (draft only)
During hexapod evolution, wings arose only once. They originated in an ancestor shared by all hexapods except the primarily wingless entognathous ones, and the insects of the Archeognatha and Thysanura, as distinct from the secondarily wingless groups such as lice and fleas, which are derived from winged ancestors. In these primarily wingless forms, the adults and young are extremely similar, except for size and sexual development, although in the Archeognatha, at least, scales and styli do not appear on the body until the third instar.
The Archeognatha and Thysanura are the closest relatives to the winged insects. The mouthparts of both orders are the simple, biting type, but in the Thysanura and all winged insects each mandible has two articulations with the head capsule. The Archeognatha retain the ancestral condition of a single link between the mandible and head. Fossils of Archeognatha and the extinct order Monura suggest that a much more extensive fauna of flightless insects lived in the Palaeozoic Era than exists today.
The adults of our species are about 12 mm long. The body is slender, tapered posteriorly, somewhat laterally compressed and arched in the front half. It is clothed in pigmented scales. In the Archeognatha the compound eyes are much larger than those of the Thysanura and meet on the top of the head; three ocelli are present. Antennae are multi-segmented, long and thread-like. On the legs, the tarsi have three segments.
The abdomen has 11 segments; the last bears a pair of long segmented cerci and a longer, segmented central filament. These “tails” are often fringed with hairs, thus “bristletails”; the “jumping” part of the name refers to the insects’ leaping locomotion. They are active, fast moving insects. They make short hops by pushing the middle and hindlegs down in unison, and by arching the body, slapping the abdomen against the ground while pushing with the legs, they make higher jumps. Modifications of the thorax and muscles unique to the group allow this leaping action.
Unlike the Thysanura, most jumping bristletails have small appendages, perhaps remnants of ancestral limbs, called styli, on abdominal segments 2-9 and usually on some coxae. These coxal styli are sensors for orientation in crevices. In the Machilidae one or two pairs of membranous, eversible, sac-like vesicles are normally borne medially on the first seven abdominal segments. They absorb water. The Family Meinertellidae often lives in desert-like environments, but evidently does not require free water.
Jumping bristletails moult 8 to 10 times before reaching sexual maturity, which may take up to two years. Adults continue to moult throughout life.
As in all primarily wingless insects, mating is by indirect sperm transfer. The male extrudes a silk thread, attaches it to the substrate and deposits spermatophores on the thread as it is formed. The female, during a courtship display, picks up these sperm packets. Eggs are laid in cracks and crevices. The simple ovipositor acts only as an egg guide.
The Archeognatha (sometimes called Microcoryphia) is a small order, containing only two families and about 450 named species world-wide and about 20 in North America. The jumping bristletails are poorly known in British Columbia and require much more study; although both the families in the order live in the province, only three or four species are recorded. These insects require much more study.
In British Columbia, jumping bristletails, unlike the introduced and domesticated Thysanura, live outdoors. Most are found in rocky places, or under wood, bark and leaf litter, especially in grasslands and dry forests. Perhaps the best places to see them are the mossy, lichen-covered rocky knolls and cliffs of the dry southern Interior and south coast. They eat lichens, algae, fungi and the bacteria and other material that abound around decaying plants and animals. Two families occur in North America. Machilidae with 9 genera and Meinertellidae with 3 genera. Both families are reported from British Columbia.
Ferguson, L.M. 1990. Insecta: Microcoryphia and Thysanura. Pp 935-949 (in) D.L. Dindale (Ed.). Soil Biology Guide. John Wiley and Sons, New York.
Sturm, H. 1991. Three genera of Machilidae from North America and Mexico: Leptomachilis, Meximachilis and Mesomachilis, with descriptions of two new sense organs in Mesomachilis males (Insecta: Archeognatha). Steenstupia 17: 53-80.
Sturm, H. and C. Bach de Roca. 1992. New American Meinertellidae (Archeognatha, Machiloidea). Pan-Pacific Entomologist 68: 174-191.