The Fascinating (but slightly horrific) Water Mite

Adult Water Mite, Homer Lake Wetland April 22, 2021

Although the title says "the water mite," there are actually something like 5000 species of water mites (out of at least 48,000 species of mites worldwide). It may be comforting to know though that only about 1500 of the aquatic species live in North America. Or perhaps not. In the photo above you can see a water mite on the underside of the leaf toward the top right. If you think it looks like a spider, you're right. Mites, like ticks by the way, are arachnids as are spiders. The most notable similarities are the two-part bodies (as opposed to three parts in insects) and eight legs (as opposed to six in insects, though apparently while in their larval stage, mites also have six... just to keep things interesting).

Mites survive the drying of the wetland and winter in the egg stage of life. When the wetland is wet again, the eggs hatch and they undergo multiple life stages... and livelihoods. In one of those life stages, the larval stage, the water mite is parasitic and for some species, the necessary hosts are damselflies or dragonflies.  In this stage, the mite larva tracks down a dragonfly or damselfly naiad about ready to emerge as an adult and attaches itself to the naiad. When the naiad crawls out of the water, splits open and the adult emerges (see post on  Dragonfly Transformation), the water mite larva transfers from the exoskeleton of the naiad to the emerging adult, finds a vulnerable place -- the new exoskeleton is not yet hardened -- grabs on, pierces the skin and begins feeding on the dragonfly or damselfly's body fluids. The water mite larvae stay attached to the adult dragonfly for some time as they feed and grow. Eventually, they will drop off into a body of water -- perhaps far from where they originated -- and continue on to the following stages of life where they become underwater predators as opposed to airborne parasites.

The photos below show a newly emerged spreadwing damselfly. The old naiad exoskeleton (or "exuvia") is visible on the plant stem above the damselfly, which is still in the process of expanding its wings. The scattering of red dots on the underside of the newly emerged damselfly, as you may guess, are not chicken pox but water mite larvae that were attached to the naiad and have now transferred and attached to the newly emerged adult (click the photo to view larger).



Newly Emerged Damselfly with Water Mites, Homer Lake Wetland, May 27, 2021

The photo below shows a mature male meadowhawk with a dozen or so larger water mite larvae attached to its underside just behind its legs (they look like small cherry tomatoes!) Studies have shown that smaller infestations like this will probably not affect the life of this dragonfly too much. This works to the mites' advantage as well. After all, they are relying on this dragonfly to continue to provide them with meals as well as free transportation to their next aquatic destination. If the dragonfly dies before they mature to their next phase of life and reach another watery destination, they will die also.  However, in more severe infestations there are undoubtedly negative impacts on the dragonfly such as not being able to successfully compete for a mate or depending on where the mites have located themselves and how many there are, possibly being physically unable to mate.


Mature Male Meadowhawk with Water Mites, Homer Lake Wetland, June 14, 2021

For the non-squeamish scholars who want to learn more about water mites, here are a couple of resources I've found informative:

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