"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

March 7, 2017

Lagaropsylla signata

One of the precondition for leading a successful life as a parasite is being able to reach your host in the first place, and various parasites have larval or adult stages that can hop, swim, or crawl towards their hosts. But there are also some parasites that need the help of other animals to get to their destination, such as the flea described in the study being featured today. This story takes place in a cave at the Gunung Mulu National Park, a UNESCO World Heritage Site on the west coast of Borneo. The cave is home to a colony of Naked Bulldog Bats.

Left: Lagaropsylla signata male (top) and female (bottom), Right: A L.saginata clinging to the leg of a cave earwig
Photos from Figure 1, 2, and 11 of the paper
While most ectoparasites can hide among the hairs and feathers of mammals and bird, this hairless bat offer no such shelter for any would-be parasites. However, that does not mean that they are completely free from ectoparasites and this is all thanks to cave earwigs. But those earwigs aren't the one doing the parasitising - they are simply passive enablers in all this, the real culprits are bat fleas

Lagaropsylla signata is a bat flea which was initially described over a century ago from specimens collected in Java, but this is the first time this parasite has been recorded in Malaysia. While L. saginata would like nothing better than dining on the blood of some hairless bats, those same bats are roosting on the roof of the cave, and the flea is not capable of scaling the cave walls to reach their hosts. Fortunately for L. saginata (but not the bats though), there are other denizens of the bat cave that a thirsty flea can turn to for help.

Enter the cave earwig Arixenia esau. The researchers found that the bat fleas were mostly either attached to those earwigs or just hanging around piles of bat guano on the cave floor, so those earwigs must have some significance for the fleas for them to be so clingy. Arixenia esau also feeds on bats - but in a different way to the fleas. Instead of tapping into the bat's blood, the earwigs are content with munching on dead skin and slurping up oils that are secreted by those hairless bats. And they are much better at navigate the cave's environment than the tiny fleas. So while these earwigs make their way to another helping of bat skin flakes and oil, L. saginata takes the opportunity to hop on board use them as a shuttle service to an all-you-can-drink banquet.

Lagaropsylla saginata is the not only ectoparasite that hitches a ride on another animal to reach their host. Last year I wrote about bird lice that hitch rides on louse flies (which themselves are also ectoparasite), and the year before that I wrote about the kangaroo leech which feeds on frog blood, but gets around by riding on crabs. Also, the human botfly lays its eggs on mosquitoes and uses those blood-suckers as a courier to deliver those eggs to suitable host, where they hatch into flesh-burrowing maggots. When you are a tiny parasite which has trouble getting around in the big bad world, you can always try and enlist the help of larger, more mobile animals!

Reference:
Hastriter, M. W., Miller, K. B., Svenson, G. J., Martin, G. J., & Whiting, M. (2017). New record of a phoretic flea associated with earwigs (Dermaptera, Arixeniidae) and a redescription of the bat flea Lagaropsylla signata (Siphonaptera, Ischnopsyllidae). ZooKeys 657: 67-79.

This paper has also been covered by Jason Bittel over at National Geographic - see his post about this particular study here.