Springtails glue, jump, and shrink when the heat rises
Collembola are the largest of three modern hexapod lineages no longer counted as insects, beside Protura and Diplura. Usually under six millimeters, they carry a sticky collophore, breathe mostly through cuticle, and can shrink about thirty percent across molts when temperatures climb.
Springtails get their common name from the furcula, a forked tail-like organ folded under the fourth abdominal segment and held in place until released to fling the animal into the air. Their scientific name, Collembola, means glue peg in Greek, after the collophore, a tube on the first abdominal segment with sticky, reversible vesicles. Early naturalists thought it anchored the body; it now appears also to take up and excrete fluid, clean the body and help steady a jump. Most species are under 6 millimetres long.
Although six-legged, they are not insects. They form the largest of three non-insect hexapod lines, alongside Protura and Diplura, and their mouthparts sit inside the head. More than 9,000 species are known. Most have no tracheae and breathe through a porous cuticle; only the families Sminthuridae and Actaletidae have a single pair of spiracles behind the head. They carry one to eight simple eyes on each side of the head unless they are blind cave or soil dwellers, and while most flee light, some are drawn to it and may navigate by polarised light.
Living in damp soil and leaf litter, these omnivores speed decay indirectly by shredding debris and regulating microbes. When temperatures climb, they can shrink by up to 30 percent over successive moults, a genetically controlled response that lowers their energy needs; soil pollution triggers the same shrinking. Their gut holds a community of bacteria, archaea and fungi in zones of differing acidity.
Rhyniella praecursor, from the 400-million-year-old Rhynie chert of Scotland, looks much like living species, suggesting that hexapods began diversifying at least 420 million years ago. Molecular data point to the globular Neelipleona as the oldest surviving branch.
Source: Springtail
