and fern spores can each reach to between . Arthropods Many small animals, mainly arthropods (such as insects and spiders), are also carried upwards into the atmosphere by air currents and may be found floating several thousand feet up. Aphids, for example, are frequently found at high altitudes. Ballooning, sometimes called kiting, is a process by which spiders, and some other small invertebrates, move through the air by releasing one or more gossamer threads to catch the wind, causing them to become airborne at the mercy of air currents. A spider (usually limited to individuals of a small species), or spiderling after hatching, will climb as high as it can, stand on raised legs with its abdomen pointed upwards ("tiptoeing"), and then release several silk threads from its spinnerets into the air. These automatically form a triangular shaped parachute which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid. The flexibility of their silk draglines can aid the aerodynamics of their flight, causing the spiders to drift an unpredictable and sometimes long distance. Even atmospheric samples collected from balloons at altitude and ships mid-ocean have reported spider landings. Mortality is high. Enough lift for ballooning may occur, even in windless conditions, if an electrostatic charge gradient is present in the atmosphere. Nematodes Nematodes (roundworms), the most common animal taxon, are also found among aeroplankton. Nematodes are an essential trophic link between unicellular organisms like bacteria, and larger organisms such as tardigrades, copepods, flatworms, and fishes. For nematodes, anhydrobiosis is a widespread strategy allowing them to survive unfavorable conditions for months and even years. Accordingly, nematodes can be readily dispersed by wind. However, as reported by Vanschoenwinkel et al., nematodes account for only about one percent of wind-drifted animals. Among the habitats colonized by nematodes are those that are strongly exposed to wind erosion as e.g., the shorelines of permanent waters, soils, mosses, dead wood, and tree bark. In addition, within a few days of forming temporary waters such as phytotelmata were shown to be colonized by numerous nematode species. Unicellular microorganisms A stream of unicellular airborne microorganisms circles the planet above weather systems but below commercial air lanes. Some microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in sea spray. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of