Marine biologist Charles Anderson noticed swarms of globe skimmer dragonflies touchdown on the Maldives throughout autumn earlier than they took off in the direction of East Africa. Back in 2009, these observations led Anderson to an attention-grabbing proposal: the migratory globe skimmer dragonfly, which is just 5 centimetres lengthy, flies seasonally from India to East Africa by crossing the Indian Ocean after which journeys again.
It is believed that the dragonflies journey on high-altitude seasonal winds to cross the ocean. Taking under consideration the dragonfly’s tiny physique dimension, this voyage could be the world’s longest common continuous migration – surpassing the gap travelled by the famed Monarch butterflies in North America.
But this epic journey is just a small a part of an enormous annual migratory circuit. It is believed that over a number of generations, globe skimmers fly between India, East Africa and Central Asia protecting greater than 14,000 km. Scientists are solely starting to unravel the small print of this circuit and the way this tiny dragonfly makes it throughout the Indian Ocean.
“It is not ‘a migration’, it is a whole web of movements,” notes Anderson, who has studied the arrival of globe skimmers on the Maldives.
While the migration of Monarch butterflies is properly studied, comparatively little is thought concerning the annual migratory cycle of the globe skimmer dragonfly (Pantala flavescens). Because of their migratory behaviour, globe skimmers or wandering gliders, as they’re additionally recognized, are distributed worldwide apart from Europe and the polar areas. A 2016 genetic research discovered excessive charges of gene move amongst populations world wide suggesting all populations can interbreed owing to their excessive dispersal skills.
“There is quite likely only one population of globe skimmers – a global population,” Anderson mentioned. “That is not confirmed, there is some uncertainty. It may be that there are two populations and if that is the case, it is likely to be the Americas and the rest of the world.”
“They are all mixing up,” Anderson mentioned.
Johanna Hedlund, a behavioural ecologist at Lund University mentioned, “The globe skimmer is much lighter than the Monarch butterfly, weighing around 300 mg whereas the Monarch weighs around 600 mg.”
“The Monarch migrates mainly over land, and what makes the globe skimmer migration from India so incredible is the hypothesis that it regularly flies over open ocean without landing,” Hedlund mentioned.
In the nineteenth century, seafarers encountered the migrants a whole bunch of kilometres offshore. Since then, people had been famous on distant islands within the Indian and Pacific Oceans leaving scientists intrigued about their migratory behaviour. Mountaineers within the Himalayas have noticed globe skimmers flying over 6,000 metres. “Extraordinary, they can fly very high,” mentioned Anderson.
Unlike another migratory bugs which are pests, globe skimmers have a constructive impact on human well being and agriculture, notes Anderson. “They do not harm people,” Anderson mentioned. “They do not eat crops. They do not spread diseases.”
“They eat other insects such as mosquitoes,” Anderson mentioned. “As larvae, they eat mosquito larvae and as adults, they eat adult mosquitoes and other insect pests.”
Belonging to an historic group known as Odonates (which incorporates damselflies), round 5,000 species of dragonflies are estimated to exist. The earliest fossils of an ancestral group of giant dragonflies return to 325 million years.
Globe skimmer migration
Flying throughout the open ocean isn’t any bizarre job for a tiny insect the scale of a globe skimmer. It requires excessive endurance and lots of perish throughout the journey. So, why do swarms of dragonflies undertake the perilous journey?
Compared with different dragonfly species, globe skimmers have an unusually quick larvae interval, reaching from egg to grownup in 5 weeks to 7 weeks. Most different dragonfly species spend a big a part of their life, a minimal of 10 months, as larvae – years, in some instances.
“For a dragonfly larva to emerge after just five, six, seven weeks in the water is actually quite remarkable,” Anderson notes. “They can do that because they specialise in [laying eggs] in warm, temporary water pools.”
“By laying its eggs in a temporary pool, which by its nature is likely to be shallow, and in the tropics, it will be warm … so [globe skimmer larvae] can grow faster,” defined Anderson. “And because there are no long-lived predators, [larvae] do not spend their life hiding under rocks and branches and holes, they are actively out hunting for food, they can consume more, they can eat more, and because it is warm, they develop more quickly.”
By the time larvae emerge as adults, it’s probably that the monsoon is over or retreating. But the flies want swimming pools of contemporary water for breeding. In search of ephemeral rain swimming pools, the dragonflies “go where the winds take them”, Anderson explains. “The potential range is so huge that if you get up into the air and drift, carried by the winds, then on average you will end up somewhere suitable.”
Globe skimmers peak in abundance in India post-monsoon, between September to December, after which they disappear. When the monsoon in India has retreated, the dragonflies are proposed to take off to equatorial East Africa the place it rains have moved to. Another era is assumed to reach in India from East Africa in spring.
While flying throughout the open ocean, globe skimmers encounter many challenges. How do these tiny bugs accomplish this feat? They have acquired morphological, behavioural and physiological diversifications for long-distance flights.
“The globe skimmer is perhaps the ultimate dragonfly flying machine and therefore the assumption is that its wings must be the very pinnacle of perfection in terms of evolutionary design,” mentioned Anderson. “So, it is assumed that the lumps and bumps, the corrugations on the globe skimmer wing are fine-tuned to promoting lift and reducing drag and these corrugations must play some part.”
“We also know that dragonflies that migrate long distances, and in particular glide, which is a mechanism for reducing fuel consumption and therefore increasing potential range, have a particularly enlarged hind wing at the base near the body so the wings are very triangular with a pointed tip,” Anderson explains.
Sanjay Sane, professor on the National Centre of Biological Sciences, Bengaluru, who research flight in bugs, mentioned, “One would expect that dragonflies have mechanisms that lock their wings and other body parts in place so that there is no energetic expenditure in actively maintaining their wing or body postures over long periods of flight.”
“The wings will also need to be structurally robust,” Sane mentioned.
Riding the wind
The Indian Ocean crossing is considered accomplished by one era in autumn and in spring protecting between 900 km to 2,400 km relying on the place to begin. However, the arrival of Indian globe skimmers in Africa in autumn and African globe skimmers in India in spring has not been confirmed but.
Globe skimmers are believed to observe a path the place high-altitude commerce winds converge, often known as the Inter-Tropical Convergence Zone, which shifts north and south seasonally. It seems as a band of clouds consisting of rain showers within the tropics.
“The Inter-Tropical Convergence Zone is extraordinarily important for the story of the globe skimmer,” stresses Anderson. A newly-emerged grownup dragonfly wants to seek out the place the rain is as a result of that’s the habitat wanted for her offspring. So, it might fly up and, beneath the affect of the Inter-Tropical Convergence Zone, could be carried by the winds. On common, the winds will take it to the place it’s raining, Anderson defined.
Sane proposes that “the powered flight could then just be used by dragonflies to rise up in altitude until they get caught in these winds, and then to descend whenever they are in sight of a major landmass”.
Because of their small dimension, tagging the flies with transmitters as is finished in birds to trace their motion is just not attainable. Instead, scientists must depend on instruments resembling radar, modeling and naturally-occurring secure isotopes of their wings to map their migration.
So, can globe skimmers fly throughout the Indian Ocean?
To reply this query, Anderson and Hedlund’s crew estimated how lengthy a globe skimmer can stay airborne utilizing solely its fats reserves. The researchers additionally used wind trajectory evaluation to find out if beneficial tailwinds can be found to move these tiny migrants throughout the Indian Ocean each in spring and autumn.
Two flight modes had been thought-about: energetic flapping and gliding flight. The former depends fully on burning fats reserves, which expends a whole lot of power, whereas the latter consumes a lot decrease power. Migration occasions from totally different websites from western India in autumn and from Africa in spring had been simulated.
The findings reveal that globe skimmers can not cross the Indian Ocean relying solely on their very own energy (energetic flapping) as they may shortly deplete their power reserves earlier than making it throughout. Even through the use of a combined technique consisting of gliding and energetic flapping, the globe skimmer dragonfly can solely full the Indian Ocean crossing on the shortest distance with an exceptionally excessive gliding velocity (9.4 km/hr) and little headwinds.
Since this situation is unlikely, beneficial tailwinds are essential to move the flies throughout the ocean. Such winds are extra out there in spring from Africa to India than in autumn from India to Africa. In autumn, solely 15% of the simulated migrations from India to Africa had been profitable, taking over common 127 hours, whereas in spring 41% of simulations from Africa to India took solely 55 hours.
“Migration in September [India to Africa] is very difficult, whereas migration in November-December [India to Africa] has many more favourable winds available. Autumn migration from the Maldives appears difficult whereas autumn migration from Gujarat seems easier. Spring migration from Africa has the most opportunities in June-July, explained Hedlund.
“A globe skimmer aiming to succeed at migrating over the Indian Ocean thus needs to have the adaptation to be able to select favourable winds,” particularly throughout autumn, Hedlund concludes.
Keith Hobson, an ecologist on the University of Western Ontario in Canada, is just not stunned by these findings. “It has been clear for a long time that for this crossing and multigenerational seasonal migration to exist in the first place, use of seasonal winds aloft is critical.” He added that “this is the first time an energetics flight simulation was conducted and “provided a more rigorous argument based on physiology”.
Sane of the National Centre of Biological Sciences discovered the research very attention-grabbing “because it suggests some new, testable hypotheses such as which locations and seasons to find the flyways, as well as perhaps testing the insects in the lab for the percentage of active flying to gliding”.
Landing at Maldives
Anderson noticed lots of globe skimmer dragonflies touchdown on the Maldives, 430 km from India, from October to December and a small quantity in spring. But there are not any freshwater swimming pools within the archipelago for breeding. In 2012, his crew traced the origin of globe skimmers within the Maldives to northern India utilizing proof from secure hydrogen isotopes within the wings of the flies. This means that the flies are travelling a distance longer than the crossing of the Indian Ocean.
So, why do the dragonflies land within the Maldives?
Scientists have no idea but however provide some probably prospects.
The world inhabitants of globe skimmers are all being swirled round by the winds, mentioned Anderson. “Some from India will follow the wind and it happens to take them past the Maldives, so they will come down and have a look and find that it is pretty useless and so they go up again and carry on and it so happens that the winds will take them all the way to East Africa.”
Hobson mentioned, “If the dragonflies are coming from northern India, it begs the question whether or not these dragonflies are using a refuelling strategy at stopover sites in much the same way we see in birds.”
Hedlund additionally mentioned, “we do not know whether arriving in the Maldives is an adaptation somewhat similar to the stop-over behaviour of birds, and that the landing on the Maldives improves survival or whether individuals that have taken the route over this archipelago are already ‘off course’ and will suffer high mortality.”
Climate change menace
Since globe skimmers want seasonally beneficial winds emigrate over the Indian Ocean, any disruption to wind patterns may have an effect on their migration. “If the movement of the Inter-Tropical Convergence Zone is sped up or delayed or advanced by climate change, then that could have an impact,” mentioned Anderson. On the opposite hand, if local weather change impacts rainfall, Anderson believes it may severely have an effect on the dragonflies.
“Many insects that are considered pests (rice planthoppers, the fall armyworm) are migratory, and it is believed that their reactive mobility enables them to disperse widely and utilise new resources where and when these resources peak,” mentioned Hedlund. “Dragonfly adults and nymphs hunt and eat many of these pests, and so it is of great importance that we do not disrupt the movement of these beneficial, predator insects.”
Many fowl species is also affected. Amur falcons, for instance, additionally migrate from India to East Africa and its route is presumed to coincide with that of the globe skimmers. It is assumed that they co-migrate together with the globe skimmer and should even prey on them en route. “If any of these birds are relying on in-flight re-fuelling – relying on the presence of globe skimmers to feed en route – and if climate change disrupts the migration for the dragonflies, then yes that would have a profound impact on the success of the crossing,” mentioned Anderson.
He will probably be taking a look at traits within the migration dates of globe skimmers. In the longer term, Anderson hopes to untangle the broader image of the migratory circuit of globe skimmers utilizing genetics and secure isotope evaluation. “There are plenty of things to be done. It is a never-ending story.”
This article first appeared on Mongabay.