"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

May 8, 2019

Antarctophthirus microchir

Lice are common parasites on birds and mammals. They belong to the order Phthirapteraand this entire order of insects have dedicated themselves to living in the dense forest of feathers and fur on those warm-blooded animals. Aside from a few species of pelagic sea skaters, lice that live on pinnipeds (the group of mammals which includes sea lions, seals, and walruses) and sea birds can be considered as the only group of insects to have successfully made a living out in the open ocean.
Antarctophthirus microchir stages: (a) egg, (b) second-stage larva, (c) adult male, (d) adult female.
Photos from Fig. 4 of the paper

Living on a pinniped poses certain challenges which are unique to that particular environment. Any external parasites of such animals would have to withstand being frequently immersed in saltwater, and not get washed away when these marine mammals propel themselves through the sea. Lice found on birds and land mammals are commonly studied because they are fairly accessible. Studying sea lion lice such as Antarctophthirus microchir and their suite of unique adaptations is another matter.

Just collecting them in the first place is a challenge in itself. How does one collect lice from seals or sea lions? They are large, wild animals, and they spend a lot of their time at sea. Previously, pinniped lice can only be obtained from dead hosts - which is not ideal for a variety of reasons. But a team of researchers have come up with an ingenious but very simple solution - a lice comb, admittedly somewhat a modified one.

In the Chilean city of Valdivia, there is a small "urban" colony of sea lions. Those are a group of sea lions that hang out around the fish markets and piers of the Calle-Calle River and they are used to the presence of people. These sea lions present a valuable opportunity for researchers to study them in more details, including their ectoparasites. To collect lice from those marine mammals, the researchers made a "telescopic lice comb apparatus" - which is basically a lice comb taped to the end of a telescopic metal rod. They selected five individuals on the basis of their skin condition and temperament to try out their new device.

The "telescopic lice comb" being deployed and a close-up of the end of the comb. From Fig.1 and 2 of the paper

They carefully approached the sea lions with their telescopic lice comb and begin combing them for lice. All this took place under the sea lion's terms - when approaching the sea lions, the researchers maintain eye contact and avoid sudden movements, and the sea lions were allowed to inspect the telescopic lice comb before the researchers start applying it to their skin.

Each sea lions were combed for 15-45 mins, starting at their head, then moving further down the body. The researchers never tried to coax the sea lions with food, and they were free to leave if they ever felt uncomfortable about the whole process. And based on how the sea lion reacted to the experience of being combed, they seemed to have thoroughly enjoyed the process, in some cases changing position so that the researchers can scratch their itchier spots.

While the "telescopic lice comb apparatus" seems to have won the sea lions' approval, how well did it work for its original purpose of collecting parasites? Well, the researchers were able to successfully collect live lice from four of the five sea lions they combed, and every life stages of the sea lion louse were present in those samples - eggs, juveniles, and adults - the lot. So they were able to obtain the entire life cycle. And in the process, they were also able to pick up some samples from the sea lions themselves including hair and dandruff.

This opens up all manner of research possibilities into the life and adaptation of these otherwise difficult to access lice. These urban sea lions may have provide science with an opportunity to study an enigmatic parasitic insect, and all that was needed to make the most of it was a modified lice comb.

Ebmer, D., Navarrete, M. J., Muñoz, P., Flores, L. M., Gärtner, U., Taubert, A., & Hermosilla, C. (2019). Antarctophthirus microchir infestation in synanthropic South American sea lion (Otaria flavescens) males diagnosed by a novel non-invasive method. Parasitology Research 118: 1353-1361