Meet Australia's Newest Rake-legged Mite

Dorsal view of Neocaeculus imperfectus, as shown in Taylor et al. (2013).

Taylor, C. K., N. R. Gunawardene & A. Kinnear. 2013. A new species of Neocaeculus (Acari: Prostigmata: Caeculidae) from Barrow Island, Western Australia, with a checklist of world Caeculidae. Acarologia 53 (4): 439-452.

And, just in time for Christmas, here comes another publication for our lab! The paper is freely available for download, and represents my first foray into the world of mite taxonomy! So let me introduce to you the Barrow Island rake-legged mite, Neocaeculus imperfectus.

One of the most productive methods that we use for our collections on Barrow Island is suction sampling. This is exactly what it sounds like: we run a blower-vac over the vegetation, slurping up any bugs that might be sitting there. This usually provides us with a ton of material relatively quickly. The method's main caveat is that it provides mostly smaller stuff (larger insects are more likely to fly away before the blower-vac reaches them, or be strong enough to hang onto the vegetation as the vacuum passes over them). You also tend to confuse on-lookers who cannot work out why you are vacuuming the scrub.

Vital equipment for any entomologist.

So the average suction sample from Barrow Island will contain a lot of micro-wasps, a lot of leafhoppers... and one heck of a lot of one particular species of mite. The entire island seems to be crawling with these guys (or girls, rather: we've not yet identified a male, and it seems likely that this species is parthenogenetic). Some samples look to contain specimens numbering in the hundreds.

Like this.

It might seem surprising for the single most abundant species in a region to also be a completely new species to science, but this is indeed what we found. This particular mite belongs to a family called the Caeculidae, the rake-legged mites. The name refers to the presence of long spines on the front legs of these mites, which they use in capturing prey. Otto (1993) observed live individuals of another species, Microcaeculus pica, and found that they would stand in once place, immobile, with their front legs raised above the ground. When a small animal such as a springtail walked underneath the raised legs, the mite would drop them down, and the spines would act like a cage, trapping the victim. This habit of remaining perfectly still goes some way to explaining another interesting detail about the Barrow Island caeculids: despite their apparent abundance, we've never seen them alive in the field (I have occasionally seen one walking about in the lab when sorting samples). Presumably their motionlessness makes them almost invisible.

Unidentified caeculid, photographed in South Africa by Jon Richfield.

Caeculids are common in many parts of the world, particularly in arid regions, but they've never gotten much love; relatively little has been published on them. A large part of this is that they're difficult to work with under a microscope, being dark and heavily sclerotised. Their aforementioned crypsis also means that they are often overlooked and may be difficult to collect. The last person to work extensively on caeculids, the now-retired French researcher Yves Coineau, reported that he collected specimens by filling a tray with leaf litter and then blowing tobacco smoke over it to make the mites move (Coineau 1974). This method would probably not be recommended today. Because of the difficulty in finding information on caeculids, we also included in our paper a key to the genera and a complete checklist of the species of the world.

Finally, in case you were wondering, 'imperfectus' is Latin for 'undeveloped'. Neocaeculus imperfectus is something of an apparently neotenous form compared to other caeculids, with adults retaining a number of juvenile features such as a low number of dorsal setae.

It's just the cutest little baby face.

REFERENCES

Coineau, Y. 1974. Éléments pour une monographie morphologique, écologique et biologique des Caeculidae (Acariens). Mémoires du Muséum National d’Histoire Naturelle, Série A, Zoologie 81: 1-299, pls 1-24.

Otto, J. C. 1993. A new species of Microcaeculus from Australia (Acarina: Caeculidae), with notes on its biology and behavior. International Journal of Acarology 19 (1): 3-13.