Sunday, December 9, 2012

Red Pond Mites: An anodyne for a gray day

A Limnesia looks on as two pairs of Piona grapple with dinner
I suppose most gardeners have noticed red mites scurrying across sidewalks and some have stopped to ponder them. One genus, Balaustium, is common enough on manmade 'rocks' that it has earned the common name of Concrete Mite. Species of Balaustium and their relatives are also called 'red velvet mites', the terrestrial members of a very diverse group (almost 12,000 described species) of often large and colourful mites in the hyporder Parasitengonina. The 'red velvet' comes from the often reddish fur and the 'Parasit-' from the peculiar lifestyle that these mites share. The first stage out of the egg, the larva, is a parasite that attaches to a host, injects enzymes, and imbibes the resulting dissolved skin and oozing fluids.The other stages are predators of other small arthropods or their eggs.
Adult of an Australian  red velvet mite (Charletonia sp.) feasting on spider eggs while sibling spiderlings look on in horror
Parasitengone larvae usually parasitize arthropods (when they bite mammals, birds and lizards, we call them chiggers). If you've seen an insect, spider, daddy longlegs or scorpions with curious blood-coloured blebs dangling from them, then they were probably parasitengones, but not necessarily larval velvet mites.  If the insect has a stage that lives in water, then the larvae are probably one of the 6,300 described (or uncounted undescribed) species of Water Mites.
Male Lestes damselfly with a cluster of red water mite larvae (Arrenurus sp.). These will eventually 'hatch' into red water mites.
Water Mites are sometimes called 'the butterflies of the mite world', but one gets a lot soggier chasing them then the typical lepidopterist does in a sunny field full of flowers. Adult water mites live in water, usually ponds, springs, streams, or lakes (a few have taken to the ocean) and swim or crawl about looking for something to eat. If you want to catch them, it's best to dress up like a hybrid of a trout fisherman and a butterfly collector - hip-waders and a very fine net.
Adult Arrenurus with several ostracods that might be dinner
If one is willing to take to the water net-in-hand, then you would have a good chance of finding lots of water mites. Each has its own preferred habitat, but sweeping emergent vegetation along the shores of lakes, ponds, and streams is an easy way to start. Dump the contents of your sweeps into a large white tray, let the muck settle, and watch for colourful red or blue dots swimming or crawling around. An eyedropper is the perfect tool for collecting the mites and moving them to a small container of clear pond water for observation.
Two Limnochares gliding past a water plant
Working out what the mites are doing for a living can be a bit more challenging, but with luck some will start catching  the copepods, ostracods, or cladocerans that are swimming around in your sample. Others may not be so cooperative, because they have more specialized feeding behaviours. For example, the large sack-like Limnochares hunt the tube-dwelling larvae of chironomid midges by searching the floors of ponds and lakes for the silken retreats of the midge maggots. When one is located, the mite creeps along the tube towards the open end and positions itself over the mouth of the tube. When the maggot's head pops out to graze on algae or detritus, the mite shoots its mouthparts out and spears the head of the midge. The much larger midge may thrash and squirm, but the mite slowly digests its brain and then feasts on the rest of its body: nature red in mite and worm.
Limnochares about to have midge maggot for dinner
Why are water mites red? Well, not all are - some are multicoloured and others mostly blue. The red colouration probably came from a common ancestor of water mites and velvet mites. The carotenoid (as in carrots) pigments that produce the red colour can help protect mites from ultraviolet radiation - essentially acting as a sunscreen. But red is also highly visible to animals with colour vision and is often associated with being distasteful or poisonous. Apparently, many water mites do make fish want to gag and they quickly spit them out and learn to avoid them in the future. It seems likely that red velvet mites also have a nasty taste. Yoder et al. (2006) have shown that when poked, Concrete Mites release a haemolyph-like fluid from a structure behind their eyes and the fluid spreads through the setae (presumably by capillary action) to cover the body. This is somewhat similar to reflexive bleeding in ladybird beetles. When the mite fluid was painted on to mealworms, predatory ants gave up trying to eat them. That is probably a good take home message - don't eat red bugs.
Don't eat red mites or bugs
References:

Proctor H & Garga N. 2004. Red, distasteful water mites: did fish make them that way? Experimental & Applied Acarology 34: 127-147. DOI:10.1023/B:APPA.0000044444.81413.1a

Yoder JA, Benoit JB, Rellinger EJ, Ark JT, Halloran MC & Gribbings KM. 2006. Structure and function of the urnulae in Balaustium sp (Parasitengona : Erythraeidae) featuring secretion of a defensive allomone and alarm pheromone. International Journal of Acarology 32: 3-12.

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