Protura (sometimes called Coneheads) are small, 0.5 to 2.5 mm long, often unknown insects which inhabit the soil and leaf litter in all parts of the world.
They are part of the Apterygota (a subclass of the Arthropoda containing 4 orders), primarily wingless insects that are very primitive with very little metamorphosis.
When we say ‘primarily wingless’ we mean that, as far as we know, these insects never had wings at any time in the past. Some insects which are now wingless are in the Pterygota (winged) section because we believe they have evolved from insects which had wings in the past.
We call this being secondarily wingless. Fleas are an example of a secondarily wingless insect.
Protura were not discovered until after the turn of the century, when they were found and recorded by two different scientists independently. The Italian Sylvestri was the first to describe them in 1907, while Berlese described some further species in 1908 and produced a monograph on them in 1909.
Since then important work has been done and published by Tuxen (1964 The Protura) and Janetschek (1970 In Handbuch der Zoologie). There was also a meta-analysis of protura research carried out in 2010 to celebrate the 100 year (or there abouts) anniversary of their discovery.
Proturan Ecology
Proturans prefer moist, organic soils which are not too acidic. Though they are generally restricted to the upper 10cm of the soil environment, they can be divided into two different groups – depending on whether or not they are found near the surface or further down.
Generally speaking, those that live near the surface have longer legs and some at least tend to be univoltine (having one generation per year) in temperate climes. Whereas those that live in the deeper realms tend to have shorter legs and appear to extend their reproductive activity throughout the year.
This situation is complicated by the existence of migratory species which spend summer near the surface and migrate down through the soil stratum to over winter.
Some species at least – such as Acerentulus danicus and Eosentomon armatum – have five pre-adult stages: a prelarva, two larval forms, a maturus junior, and a preimago, Tuxen (1949).
Unfortunately not much is known of the feeding habits of proturans. Their mouthparts are styliform, suggesting that they are fluid feeders and their is evidence that some species feed on the contents of fungal hyphae.
Protura Identification
Protura are easily recognised because they have no (or very reduced) antennae, no eyes and have limb-like abdominal appendages on the first three abdominal segments as well as the normal three pairs of thoracic limbs.
They hold the first pair of legs out in front of them and use them as antennae. They have 8 abdominal segments and a telson when they first hatch. However 3 more abdominal segments develop later to give a total of 11 (this postembryonic increase in the number of abdominal segments is a common characteristic of arthropods). They have no cerci.
Taxonomy
There are 500+ species of proturans known at the moment, 17 of which occurr in Britain. They are divided into two superfamilies each containing two families.
Super Family Eosentomoidea
- Eosentomidea (contains one genus Eosentomon)
- Sinentomidea (contians one primitive species Sinentomon erythranum)
Super Family Acerenotomoidea
- Protentomidea (Contains 3 genera Hesperentomon, Proturentomon and Protentomon)
- Acerentomidea (Contains 10 genera including Acerentulus Acerella, Acerentomon and Berberentulus)
What Next?
Well, I hope this has been an interesting little look into the strange world of the cone heads!
Perhaps now you’d be curious to learn more about ice bugs.
Feature Image license: Creative commons
