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Minuscule Hitchhikers Pinch a Ride

Creature Feature - Pseudoscorpions

These small arachnids are all around us, and may even live in your house!

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Fig. 1 This tiny critter spins silk, incapacitates small insects with venom from its claws, and may even live in your house. Photo by Kyron Basu, BugGuide.net.

I came to school to study birds, and as luck would have it many birds eat bugs, so now I spend most of my time with bugs. I thought that this shift in subject would be a total bummer, completely boring, and let’s be honest – gross. Bugs can be pretty terrifying, especially if you don’t understand their behavior and why they have such odd strategies for life.

One day, I was dumping out a jar full of preserved bugs from some forest leaf litter I’d collected from one of my field sites. I put the insects under a microscope and was shocked to see what looked like an adorable, teeny tiny scorpion. But wait - It couldn’t possibly be a scorpion! I collect my samples in Massachusetts, not a desert state in the southwest. Also, this scorpion seemed to be missing its tail. As I kept encountering more and more of these tail-less individuals, I realized that this must be something entirely different.

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Fig. 2 Three individuals, each smaller than a grain of white rice! Photo by Kit Straley.

They’re called pseudoscorpions, belonging to the Pseudoscorpiones group of arachnids related to true scorpions and spiders. There are over 3,500 species of them worldwide [1], a whopping number when you consider that there are less than 300 species of mammals belonging to the Carnivora group [2]. North America in particular has approximately 420 species [3].

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Fig. 3 Figure from Buddle (2010) illustrating the diversity of pseudoscorpions in size, shape, and color [2].

These creatures are incredibly diverse and exist worldwide [3,4,5]. Despite their high levels of diversity, they are rarely seen because they live under bark or stones, in leaf litter or mosses, and between the boards of buildings [5]. One particular species even lives in houses, hunting the small insects that would otherwise be house pests [4]. Should we be scared? After all, they do have pinching claws that produce venom [3].

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Fig. 4 Close up of a “thoughtful” pseudoscorpion. Photo by Dennis Spamlin, Flickr.

Pseudoscorpions are not harmful to humans, and are in fact helpful! They do not damage property, eat tiny pests like mites, and their venom is not dangerous to us in such small amounts [4].

Now that we’ve gotten that concern out of the way, let’s focus on what makes them so incredibly cool: their behavior. Pseudoscorpions are tiny [5]. Individuals that are the size of rice are actually the LARGE ones. It must be tough for creatures so small to move long distances on their own. So how do they get around to far away places? Do they contently reside in the same patch of moss? No!

They hitch a ride [3,5,6]. Pseudoscorpions have been documented hitchhiking on all kinds of flies and beetles. In one particular study of their hitchhiking, scientists found that males even BATTLE IT OUT on the backs of beetles to establish mating territories should a female hop on [6].

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Fig. 5 Pseudoscorpions hitching a ride on flies. Left photo by Tom Murray, right photo by Nick Block, BugGuide.net.

For mating, males deposit sperm packets on the ground for the females to pick up. Sometimes she finds it on her own, sometimes he helps her out by leaving a trail of silk to guide her, and sometimes he just straight up drags her over the sperm pile to make sure she doesn’t miss it [4]!

The female can use her silk, which unlike spiders does not come out of her rear end but rather her claws (true spiderman-style), to build a hidden retreat while she tends to the eggs [4]. Males can spin silk, not only to help females find sperm but also to build secluded spaces in which they overwinter [4,5].

What an awesome and hilarious creature. So far I’ve only gotten to see them in my preserved samples, under a microscope. One day I hope to see a live pseudoscorpion out there in the woods, riding his majestic beetle steed, hoping to impress a lady.

For more information on pseudoscorpions, check out this blog post by Christoper Buddle (http://www.scilogs.com/expiscor/ten-facts-about-pseudoscorpions/) or any of the sources at the bottom.

References:

  1. Harvey, M.S. “Order Pseudoscorpiones.” In: Zhang, Z-Q. (Ed.) Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013). Zootaxa 3703, no. 1 (2013): 34-35. http://dx.doi.org/10.11646/zootaxa.3703.1.8.

  2. Buddle, C.M. “Photographic key to the Pseudoscorpions of Canada and the adjacent USA.” Canadian Journal of Arthropod Identification 10 (2010):1-77. doi:10.3752/cjai.2010.10.

  3. Bartlett, T., R. McLeod, C. Wirth, C. Entz, G. Montgomery, C. Eiseman, J.C. Trager, and V. Belov. “Order Pseudoscorpiones – Pseudoscorpions” [Internet]. Iowa State University Department of Entomology, Ames, IA. (2014). http://bugguide.net/node/view/2892.

  4. Evans, A.V. “National Wildlife Federation Field Guide to Insects and Spiders of North America.” Sterling Publishing Co., New York, NY. (2007). pp 409. http://www.amazon.com/National-Wildlife-Federation-Insects-Spiders/dp/1402741537.

  5. Triplehorn, C.A. and N.F. Johnson. “Borror and DeLong’s Introduction to the Study of Insects,” 7th ed. Thomson Brooks/Cole, Belmont, CA. (2005). pp 135. http://www.amazon.com/Borror-DeLongs-Introduction-Study-Insects/dp/0030968356.

  6. Zeh, D.W. and J.A. Zeh. “On the Function of Harlequin Beetle-Riding in the Pseudoscorpion, Cordylochernes Scorpioides (Pseudoscorpionida: Chernetidae).” The Journal of Arachnology 20, no. 1 (1992):47-51. http://www.jstor.org/stable/3705790?seq=1#page_scan_tab_contents.

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