… a blog written by Sarah Hawkes, Buglife’s Natur am Byth! Scarce Yellow Sally Conservation Officer. (view this page in Welsh)
What insects migrate?
Butterflies and moths: Painted Ladies (Vanessa cardui) and Monarch (Danaus plexippus) butterflies migrate, so do Red Admirals (Vanessa atlanta). What about Clouded Yellows (Colias croceus) or white butterflies, (Pieris spp.)? They’re all long-distance migrators. Amongst the moths there are Silver Y (Autographa gamma); which once crowded into Stade de Paris during the 2016 Euro Final when Ronaldo was playing. But many more make long journeys. In Europe they include Rush Veneers (Nomophila noctuella), and Death’s-head Hawkmoths (Acherontia atropos), Convolvulus Hawkmoths (Agrius convolvuli) and many others.
Beetles: Fewer beetle species migrate, but some do. However, sea crossings are challenging for beetles. Nonetheless, Seven Spot ladybirds (Coccinella septempunctata) arrive on the southern coastlines of Europe and the UK every summer in varying numbers often affected by the weather at sea.
Bumblebees: Bumblebees are not, so far as we know, long distance travellers but there is strong evidence for dispersal behaviour and a sort of proto-migration amongst Buff-tailed Bumblebees (Bombus terrestris) across the North Sea from the UK and making landfall on the Dutch coast during years of population growth further north and east.
Dragonflies: Famously the Globe Skimmer (Pantala flavescens) dragonfly travels immense distances – an annual migration from the Himalayas to East Africa – crossing the Indian Ocean!
Flies: These are some of the most remarkable migrants of all. The sheer numbers that move across continents are almost incredible. Hoverflies like the familiar Marmalade Hoverfly (Episyrphus baleatus), about one centimetre long, will set off south in autumn and, in one single journey, stopping only to snack along the way, head straight to their over wintering grounds around the Mediterranean and beyond. But even hoverflies are not the smallest self-powered migrants. There are some tiny grass flies (Chloropidae) just a couple of millimetres long that also lift off and head south from our UK shores.
Lesser Emperor Dragonflies (Anax parthenope) setting off from the southern coast of Spain, near Malaga, across the Mediterranean to Morocco © Will Hawkes
Are migrating insects ‘self-powered’, really?
You could rightly question this because ‘surely such a tiny insect is at the mercy of the wind.’ Well, the right winds are important, but their flights are not chance journeys at the mercy of fate but deliberate, regular journeys very often in the company of many others of the same species. These insect journeys are like the well-known bird migrations and birds often travel with insects, using them as a sort of travelling lunch box.
So, with that lunch box habit in mind, why do insects take the risk of a long journey?
Migration is a useful way of giving your species options for survival through difficult times. In fact, many migratory insects (such as Eristalis hoverflies) utilise both migration (to escape a possible hard winter) and staying put (to maximise their chances for a head start if there is a mild winter). If the ‘stay-at-homes’ lose their bet and it is a bad winter, then having a population that overwintered in warmer, lusher lands justifies the risky journey. You may find the home populations of Eristalis hoverflies overwintering in crannies around cave mouths and similar places during the winter months.
Flyways
There are many ‘flyways’ south and many routes north. In fact, all around the planet insect migrations are happening. The Monarch Butterflies of North America are well known, but also there are hoverflies and others moving north and south along the eastern seaboard of Canada and America.
One of the most amazing journeys is the enormously long flight path of the Globe Skimmer dragonfly. This beautiful creature flies (for one of its routes – there are more!) south from at least the Himalayas, on across India, to the Maldives and then bears right to East Africa where their arrival is the stuff of joyous legend, forecasting the arrival of the rains.
Why? Well, it turns out that the monsoon rains and a desire to escape predation are the key drivers. The Globe Skimmer has adapted its life cycle to this route to stop predators getting its young. This dragonfly’s larval stage is much shorter than the normal dragonfly habit of years as a water- living larva. Globe Skimmer young go from egg to adult in weeks. This enables them to exploit predator-free freshwater monsoon puddles that dry up once the rains have passed.
So, on to the crux of the problem that is emerging for the world.
Migratory insects are moving north and south, east and west, as always, but in ever fewer numbers. There are billions of insects arriving in the UK every year and billions leaving, but 50 years ago when the Lacks noticed the migration, there were hundreds of billions.
As they cross Europe, insect migrants are struggling to find habitat to feed and breed in. Once abundant and connected, habitats are now few and far between. More housing, factories, more polluted air and water, more pesticides and herbicides in gardens and farms, means fewer insects will make it all the way north and the cycles of nutrients, pollination, and biodiversity balance (such as, from our human view, eating aphids before the numbers get out of control) are reduced. As habitats become more disconnected, the cycle of nutrient transfer to the land is disrupted, our insects and soil fauna are less abundant, and less diverse and the nature all species rely on is poorer.
How do we revive this vital ecosystem?
We can restore the habitats that insects need to survive and thrive. We can reconnect these habitats at a landscape-scale, at a continental-scale, so insects can move freely across huge land masses on their annual migrations. One way to do this is through Buglife’s B-Lines initiative – which is all about connecting habitats for pollinators and other wildlife: buglife.org.uk/our-work/b-lines/
We can restore nature, but we need to be bold, and we need to act now.
Join us in the second part of our blog for ‘A story of a migration out of Wales’, next week.
Main Image Credit: Migration over the Pyrenees © Will Hawkes
