by Leslie Cox; Wednesday; November 23, 2016
Nothing like a string of really miserable wet days to encourage you to take a look at some of the garden photos you took on sunny drier days. Wonderfully medicinal…although I am getting a little itchy to go outside and stick my hands in the soil.
I was saved from a serious soaking by a strange creature I photographed at one of my school gardens, back in September 2011. Had forgotten all about him. (Guess stormy, rain days are good for something…especially when I hate housework!)
Meet a bristletail…also known as an Archaeognatha, and closely related to silverfish and firebrats. (The latter two are classified in the order Thysanura.)
Before you say “yeeeeoooww”…let me also add: the bristletail is a beneficial insect, where the other two are not, so much. Another nice feature: bristletails prefer to live outdoors, where silverfish and firebrats like to invade the warmth of our homes.
Most Archaeognaths are found in wooded, grassy, or herbaceous habitats where they hide under leaf litter or bark. Most active at night, they feed on mosses, lichens, algae, and decaying matter. There are also some species which prefer a more seaside habitat, living happily amongst the stones and debris at the high tide mark.
Bristletails are an order of wingless insects…one of the longest lived and evolutionary-wise, amongst the least changed. A partial fossil of what is thought to be an Archaeognatha was discovered in the Gaspe Peninsula in Quebec in 1988. Carbon dating has pinpointed the age of the fossil at 390 to 392 million years old which places it roughly in the middle of the Devonian era. However, because it is only a partial fossil, some scientists are discrediting its actual identity as a bristletail….although the argument is still ongoing since a later fossil discovery of another species in the Archaeognatha order has been pinpointed to the early part of the Devonian era and provides a possible link between the two fossils.
Geography Byte: Did you know…roughly 400 million years ago, the northern shoreline of the Gaspe Peninsula used to lie at 10° latitude? On today’s global map, that would place it just north of San Jose, the capital of Costa Rica, in Central America.
One of the physical features which sets Archaeognaths totally apart is their mouthparts. It is unusual because their mandibles are monocondylic…they connect to the head in only one place. The mandibles of all other insects are dicondylic…they connect to the head in two places.
Other physical characteristics…their body is elongated and roughly cylindrical in shape. The thorax shows a definite hump and their whole body is covered in thin, tiny scales. They have large compound eyes which meet in the middle of the head. There are also three ocelli, or little eyes…simple, light detecting organs. Usually grey or brown in colour, they have six legs, long flexible antennae, and three long tails with the middle one being the longest.
A few unique features of Archaeognaths sets them apart from silverfish and other species in this family. These include several small, bendable “styli” found in the middle and hindmost sections which are thought to be rudimentary appendages. They also have eversible membranous vesicles…sacs which are capable of extending and turning inside out… along both sides of their body which are specifically designed to absorb water, or moisture from their environment. Another unique feature is their ability to jump up to 30 cm (12 inches) by using their long tails. This helps to keep them out of the jaws of predators.
Digging into their life cycle…there is little metamorphic change during the nymph stages, once the eggs have hatched. Archaeognaths progressively molt through six instar stages to reach adulthood and most references claim they can live anywhere from four to eight years.
Bug Byte: Bristletails must anchor themselves to the forest floor, or substrate, before they begin to molt. If the fecal material they use as an anchoring cement to hold themselves in place through the molting process should fail to hold, the bristletail is not able to complete its molt and will die.
Sexually, the Archaeognaths are also a little different. Males and females do not copulate to reproduce. Rather, once they reach sexual maturity…possibly taking as long as two years…the males produce a string of spermatophores (tiny packets of sperm) on a spun thread from their abdomen. The threads are somewhat haphazardly attached to the substrate in locations where a female is likely to stumble across it…although there are some species where the males will do a courtship dance to entice a female to their spermaphores. The aroused female picks up a packet of sperm and deposits it on her ovipositor. Depending on the species, the female will lay her eggs in a suitable crevice…either singly or in batches of up to thirty eggs.
Little else is really known about these bristletails…other than they can be found on every continent, including the Artic and Antarctica. So, given their naturally shy nature…despite their extensive geographic range…I feel especially privileged to have spotted one in broad daylight when I just happened to have my camera handy!
