What is this creature?

By Chris Williams on May 7, 2015.
millipede on hardwood floormillipede in house

This was the title of an email I received from my niece with an attached video.  She said it was crawling on her bedroom ceiling. Is it a centipede? I just looked at it for a second and said yep, but then giving it a second look, it is actually a millipede.  So the question then is: why is it in her home?

What are millipedes?

Well, because they have more than six legs, they’re not insects. They are not in the Arachnid class (spiders, scorpions, etc.) either. They are their own class in the arthropod world known as Diplopoda. These unique creatures have two pairs of legs on all but their first three body segments. That is up to 375 pairs on some of the longer species! Not quite one thousand legs as their nickname “thousand leggers” suggests, but 750 is a lot of legs! According to (used here for reference), less than ten thousand species have been described worldwide, but there may be many thousands more yet to be discovered.

How do millipedes make their living?

Around the home they typically live in moist, protected sites like mulch, beneath rocks or other objects.  They feed on dead plant material (e.g. leaf litter, perennials that dieback, etc.) helping to decompose and recycle it. Though millipedes are not usually a major pest issue, from time to time they do invade indoors, and often in large numbers. This migratory behavior supposedly coincides following periods of rainy weather, but I’m not so sure about that.

I have one client that has gotten invaded regularly for the past five seasons at just about the driest point of the summer. What makes this behavior even more strange is that the homeowners do not have a lot of heavy shade (which would raise humidity) around the structure, and they don’t use organic mulch like shredded bark, but rather crushed stone instead. They also recently did extensive modifications to the basement to make it completely dry. They’d done everything they could to discourage them from thriving around the outdoors, and yet dozens of them invaded. What is a really bizarre about these types of invasions is that it is almost like a mass suicide, because millipedes require high humidity to survive. Oh well, if there is any upside at all to these kinds of incidences, it’s that millipedes are merely a nuisance and completely harmless. Break out the vacuum cleaner and you should be all set!

Top image: Whitney Cranshaw, Colorado State University, [CC BY 3.0], via Wikimedia Commons



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