Amanda Maxwell

Aug 21st 2020

How Do Insects Migrate?


Vespa mandarinia, an invasive species known as the murder hornet, are resurfacing in the West Coast. According to the New York Times, these giant hornets have been identified in Washington state and over the border in British Columbia, Canada.

Although these particular travelers probably hitched a ride across the Pacific by packing crate, people have started to wonder, just how do insects migrate?

Insect Migration Routes

Murder hornets are much bigger than the native species in North America, clocking in at around 4 to 5 cm (almost an inch) in length. The BBC describes how they decapitate entire beehives to feed their young. Although some may have hitched an airborne ride with commercial freight, aerial migration is unlikely. According to Business Insider, accidental introduction is much more likely.

But other insects do show impressive migration routes. Apart from learning the life cycle of the Monarch butterfly and its 3,000-mile journey, few people consider how insects migrate. Unlike flocks of birds or herds of wildebeest, they’re difficult to follow. However, researchers are finding new ways to monitor their migration and are discovering some amazing facts along the way.

Hydrogen Isotopes and Radar Scans

Hydrogen isotope research has revealed where green darner dragonflies start their 900-mile migrations each spring and fall. Washington Post describes how University of Maryland Baltimore County researchers analyzed wings from collections across North America and the Caribbean, looking at the hydrogen isotope signatures for the birth ponds of larvae. Data show origin ponds in Florida, Maryland and Maine.

Meanwhile, in the U.K., hoverfly migrations show up on radar. The New York Times shows how researchers clued in on the unique radar signature that these tiny wasp-like insects possess to track their migration. Using the data captured from insects flying at elevations higher than 450 feet, the scientists estimated 4 billion hoverflies cover around 50 to 100 miles per day.

How Do Insects Migrate, and Why?

Researchers know that some migrations are intentional and directional. For example, Bogong moths in Australia appear to navigate hundreds of miles. A paper in Current Biology reveals that moths probably combine visual landmarks and nighttime starscapes with cues from the Earth’s magnetic field to make the 1,000 km (around 621 mile) journey between breeding grounds and seasonal cave shelters.

Bogong moths migrate to stay safe from predators, sheltering in caves during their seasonal aestivation or dormancy period. Many insects migrate to reach breeding grounds that have abundant food as well as good weather conditions. Since insects are cold-blooded, many need warmth for activity.

Migrating specifically for food sources is seen with a lot of pests and predatory species. In British Columbia, Natural Resources Canada describes how mountain pine beetles flit from tree to tree in order to feed off sap. When healthy evergreens are scarce, the beetles can migrate up to 100 km (ca. 62 miles) in search of fresh trees, damaging tracts of valuable forestry along the way.

Impact of Insect Migration

Pest insect migrations damage crops and other important natural resources, altering the ecosystem for other species as well as harming food production. For example, murder hornets prey on honey bees and can destroy entire hives within a few hours. This is why it’s often important to control invasive species. However, insect migration can also control pests; samurai wasps in the U.S. help keep stinkbugs under control.

As well as moving the boundaries for important pests and predatory species, climate change also impacts migratory routes. The National Resources Defense Council notes that climate change is impacting dragonfly migrations. Warmer temperatures could mean that green darners may not need to migrate at all in the future.

As well as missing out on seeing dragonflies flitting around, reduced migration northwards impacts the ecosystem. Fewer dragonflies on the buffet mean lean times for frogs, ducks and carnivorous plants, for example. It also means that other winged insects such as aphids and mosquitoes, which are part of a dragonfly’s diet, go unchecked.

In southern England, hoverfly migration moves around an estimated 80 tons of nutritious biomass; losing the migratory routes could deprive predators of around 35 million calories. It would also impact pollination vital to many food crops.

Migrating insect biomass not only supports species diversity but helps put food on our tables.