Thursday, June 16, 2016

Maryland: Weird and Wonderful - Millipedes, Mycosis, and Mind-Control

"Maryland: Weird and Wonderful" is a WMD101 series showcasing specific natural phenomena occurring in Maryland that are particularly interesting or unusual.

An infectious pathogen slowly takes hold of its unfortunately victim.  Doomed to die, its host mindlessly crawls upward. No longer in control of its own body, its only mission is to infect other members of its species. 

It sounds like the plot of a zombie movie, but this same story plays out on a much smaller scale within the forests of Maryland. In this case, the hapless victims are flat-backed millipedes (Apheloria virginiensis corrugata) and the deadly pathogen is a entomopathogenic fungus called Batkoa. 

Dead flat-backed millipedes cling atop the branch they were compelled to climb.
Harmless to humans and most other animals, this fungus species does little to affect its millipede host until it is a sufficiently-sized adult.  When the temperature and humidity is just right, the fungus releases chemicals that compel the millipede to leave its safe habitat beneath the leaf litter, climb atop fallen logs and branches, and grasp these perches tightly.  The fungus then consumes the internal organs of the millipede and pushes through the creases of its exoskeleton, releasing its spores into the air.  Carried by the breeze that hits the top of the logs, the spores disperse over a large distance. Having landed, the spores lie dormant in the leaf litter, waiting to be accidentally ingested by another millipede. 

Notice the puffy whitish fungus emerging between creases in its exoskeleton. 
The purpose of Batkoa's "mind-control" is clear - if the millipede were to stay beneath the leaves, the spores would be trapped in a small area.  Many entomopathogenic fungi use this strategy of compelling their hosts to climb to conspicuous locations during their spore-bearing phase.  It's so common, the behavior even has its own name - "summit disease" - for the tendency of the dying arthropods to seek out the summits of rocks, logs, and plants so the spores may catch the wind. 

Despite their life-like poses, these millipedes are quite dead - they are even hollow inside!
If you are hiking in the spring or fall, be on the look-out for precariously perched creepy-crawlies - you may find the victim of a morbidly fascinating fungus!



Cornell University Plant Pathology Photo Lab

Herlocker, David

Maryland Biodiversity Project

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