Archeognatha

Common Name: Bristletails

Greek Origins of Name: Archeognatha, derived from the Greek “archeo” meaning ancient and “gnatha” meaning jaw, refers to the primitive (monocondylic) manner in which the mandibles connect with the head capsule.

Spot ID Key Characters:

Apterygote (primitively wingless)
Three terminal filaments, dissimilar in length including short cerci and a longer median caudal filament
Compound eyes large
Body cylindrical, no scales

Development:

Ametabola, i.e. lacking metamorphosis; eggs hatch into young which are smaller than adults, but similar in appearance.

Taxonomy:

Apterygota; primitively wingless

Distribution:

Common in grassy or wooded habitats worldwide. Approximately 2 families and 20 species in North America and 2 families and ~350 species worldwide

Life History and Ecology

Most bristletails live in grassy or wooded habitats where they are most likely to be found in leaf litter, under bark, among stones, or near the upper tidal line in coastal areas. They are most active at night, feeding as herbivores or scavengers on algae, mosses, lichens, or decaying organic matter.

Sexual maturity is reached after at least eight juvenile instars spanning up to two years. Molting continues periodically even after adulthood. The sexes are separate, but copulation does not occur. Males produce a packet of sperm (spermatophore) and leave it on the ground to be picked up by a female. Females cannot store sperm (they lack a spermatheca), and evidently acquire a new spermatophore before each bout of egg laying. Eggs are laid singly or in small groups (<30). Some species have elaborate courtship rituals to insure that females are able to locate a spermatophore.

Appearance of Immatures and Adults:

Body cylindrical in shape and tapered posteriorly
Thorax somewhat arched dorsally
Compound eyes large, often touching; ocelli usually present
Antennae long, thread-like, and multisegmented
Tarsi 3-segmented
Abdomen with ten complete segments
Eleventh abdominal segment elongated to form a median caudal filament
Cerci present, shorter than median caudal filament
Short, lateral styli (rudimentary appendages) present on abdominal segments 2-9

Economic Importance:

Bristletails are common inhabitants of forest leaf litter. They are part of the community of decomposers that break down and recycle organic nutrients. None of the Archeognatha are considered pests.

Major Families:

Machilidae (Jumping Bristletails) — most of the North American species belong to this family. They are common in the leaf litter of deciduous forests and on rocks near the seashore.

Fun Facts:

Some bristletails can jump up to 10 cm (4 inches) by snapping their abdomen against the ground.
Before molting, bristletails must fasten themselves to the substrate. If the fecal material used for cement fails to hold, the insect is unable to complete the molt and will soon die.
Most bristletails have eversible vesicles on abdominal segments 1-7. These structures evidently help maintain the insect’s water balance, probably by absorbing water from the environment.