November 13, 2007

A Mite is a Mite is a Mite? Not Quite!

worm bin mites

Apologies for the lapse in posts lately! Lots on the go these days, but still aiming to be much more active in coming weeks and months.

Today I wanted to chat about worm bin mites. Pretty well everyone who sets up their own home system is bound to encounter mites at one time or another. Many people tend to lump them together as a group (ie. “I have mites”) and assume they are ‘bad’ – especially when there is an abundance of them.

Well, mites are of course a ‘group’ – they belong to the class Arachnida (along with spiders) and the subclass Acarina – but they are a hugely diverse group, with thousands of species occupying many different niches and serving a wide array of functions. They are found in abundance both on land and in aquatic habitats.

They are among the smallest of the arthropods (the group that includes crustaceans, insects, mites and spiders – among others), and thus are often over-looked. This also helps to explain why people have difficulty distinguishing different varieties in their bins. According to Walter & Proctor (1999) the highest diversity of mites occurs in soil and decaying organic matter – apparently a handful of forest soil can contain as many as 100 different species (and many thousands of individuals).

Mites can be predators, detritivores, herbivores, and parasites. Some (predator) species are widely used as biological control agents, feeding on a wide array of different plant pests. Generally speaking, most mites found in a compost heap (or worm bin) are relatively harmless, simply feeding on decaying organic matter.

Let’s now chat about some of the varieties you can encounter in your bin. This is purely based on personal observation, and thus not scientifically validated. 🙂
My descriptions are based mainly on colour, body shape and speed of locomotion. I’m hoping to study mites a lot more in the future and will hopefully be able to add to this info at some point.

Flattened / Fast moving / Light Brown – These are usually predatory mites. I actually bought some Hypoaspis miles (a predatory biocontrol agent) once in an attempt to deal with a really bad fungus gnat infestation I had in a couple of my bins. They were very small, light brown in colour, and very fast! I’ve seen similar mites in outdoor manure and compost piles, and sometimes in my indoor bins as well. Predatory mites are of course encouraged in a worm composting system since they can feed on other creatures typically thought of as pests.

Reddish-Brown / Slow moving – Mites like the one picture above on the left seem to be fairly common in my worm bins. They seem especially attracted to water-rich cucumber family fruit (or vegetables – however you choose to look at it). The photo above was actually taken on a watermelon rind (during my coffee cup challenge), but I’ve seen lots on squash as well. I’ve actually read that putting some watermelon in your bin is a great way to get rid of them (if you have a major infestation and are worried they are competing with your worms for food). Simply leave the melon to sit for a day or two then remove it (presumably with a huge number of mites attached). For the most part, these mites won’t cause your worms any harm other than potential competition.

White Shiny Round Mites / VERY slow moving – many people report seeing lots of “eggs” in their bins. Most of those who have not yet seen a worm cocoon (which is much larger) assume they are ‘worm eggs’, and I’ll even admit to being fooled into thinking they are the eggs of some other creature. Upon closer examination, you will see that they are in fact mites. This type of mite (which may in fact be a couple different varieties – as the pictures above almost seem to suggest) is sometimes assumed to be a worm predator or parasite since they sometimes found covering worms. The only times I have seen this myself has been when my worms were dying or dead already – the mites seem to be scavengers (like little worm bin vultures – haha). I currently have quite a few of these (or at least a similar variety), but they seem to be attracted to some squash segments I’ve been composting (for an upcoming video).

Those are the main groups of mites I have encountered indoors. In outdoor systems there will definitely be a much greater diversity of species.

One other variety I should mention. There is apparently a ‘red mite’ that is parasitic on adult worms and eggs. Infestations of this mite seem to occur in the beds of worm farmers on occasion. The only (academic literature) records of parasitic mites – on worms that is – I could find were those species that parasitize worm eggs (not adults). Bottom-line, you definitely don’t need to worry TOO much about the parasitic varieties. There haven’t been all that many cases reported from the sounds of things.

Here are some additional thoughts and generalizations about worm bin mites…

They seem to like high moisture conditions and water-rich foods. An population explosion of mites in your system(s) could be an indication of over-feeding, or of your worms dying (which could of course occur if you were over-feeding). Again, for the most part you don’t need to get too stressed out about mites in your bin. Be assured, they are there to serve a function, and may simply indication that your system has shifted out of balance somewhat. In fact, they often appear in abundance early on when systems are not yet balanced.

Ok, thats all for now. Be sure to share any interesting mite experiences you might (or should I say ‘mite’ – yuk yuk) have had as well!

Walter, D. and H. Proctor. 1999. Mites: Ecology, Evolution & Behavior. CABI Publishing, New York. 322pp.

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