Insect Migration: Whose the Winner?

Hola!

I was taking a break from studying for finals when, for some reason, I though about insect migrations. Not sure where this was going to take me, I did what anyone who likes to procrastinate would do: Google "Insect Migrations." This didn't satisfy my appetite for random knowledge, so I decided to "up the ante," so to speak. Which insect was found to have the longest migration? I honestly thought I'd be writing this blog on the famous Monarch butterfly (Danaus plexippus), which flies from North to South America each year (about 7,000km round trip), but behold! A new record breaker has come to take that crown!

I found a cool BBC article from 2009 that discusses how millions upon millions of dragonflies fly from southern India to Africa...crossing the Indian Ocean while they're at it! It hasn't been completely confirmed, but Biologist Charles Anderson has been studying these insects (from the order Odonta) for years and has already published a journal about it in the Journal of Tropical Ecology. While working in the Maldive Islands for marine research, he noted the dragonflies when they arrived in 1983. It was a peculiar site for him; the islands lie 500 to 1000km away from the India mainland. In addition, dragonflies requre freshwater when they lay their eggs, but the 1200 island cluster are all coral cays--there's hardly any freshwater available on land!  Since this peculiar sighting, Anderson has been keeping track of their arrivals and departures.

Picture 1: Imagine flying from India (left part of yellow)
 to eastern Africa (brown) without an airplane!

Anderson researched and found that each year, the dragonflies arrive in waves on the islands around mid October. The numbers escalate until December, and they fly off once more. The insects will only stay for a few days before taking off again. A weather system, called the Inter-tropical Convergence Zone, is probably what helps them fly towards the islands. The winds following the ITCZ blow steadily towards East Afrca, providing a guide for the dragonflies to head towards the other continent. During their flight, they glide on the winds, consuming small insects along the way.

More research was conducted to see if this journey was valid. Observations were done on the individual species taking this journey; 98% of the swarming dragonflies consisted of Globe skimmers (Pantala flavescens). Not only is this species found in India and the Maldives, they can be seen at certain times in eastern and southern Africa. They appear twice each year (March-April and September) in Uganda and are noted in Tanzania and Mozambique during December and January.

Picture 2: A Globe skimmer (Pantala flavescens) in action.

In total, these dragonflies will take a round trip of 14,000 to 18,000km over four generations of insects! What drives them to perform this feat, you ask? It is suspected that the dragonflies follow the heavy rains that the monsoons of Africa and India bring. They will follow these weather systems, completing their life cycles along the way. Many migratory birds also take advantage of these weather systems; cuckoos, nightjars, falcons, and bee-eaters take the same path as these dragonflies do. All of these birds are medium-sized with a diet consisting of insects like dragonflies, thus presuming that they eat the dragonflies while they fly. How convenient!

This is quite the journey for animals with only a schlerotised exoskeleton protecting them from the harsh conditions outside! I mean, dragonfly wings are sturdy, yet delicate; crossing the Indian Ocean for thousands of kms must be pretty taxing on the insects! It really does blow my mind how much we don't really know about the natural world and its limits.

With that said, I now pronounce the crown of the Longest Insect Migration to the Order Odonta!

 ~Mel

You can find the article at:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8149000/8149714.stm

Picture 1:
http://files.ctia.org/img/polmap/world_map.jpg

Picture 2:
http://leesbird.com/2009/07/18/it-dragonflies-ii/