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The Mysterious World of the Microblind Harvestmen By JOE EATON Special to the Planet

Tuesday October 04, 2005

Microcina leei may very well be the most obscure creature I’ve ever written about. It stumped Google Image; the accompanying photograph is of a very distant relative. It’s only a millimeter long and spends its entire life hiding under rocks. 

Why is it worth the column inches, then? Well, for openers, it’s a Berkeley near-endemic, found only at one site in the hills above campus and another just beyond the Oakland border. Few other creatures, if any, can claim that distinction. It’s also a presumptively endangered species that’s been left out in the cold by the machinery of protection. And it and its relatives pose an intriguing puzzle for students of biogeography, the science that tries to determine why living things are where they are.  

M. leei and its six fellow members of the genus Microcina are known as microblind harvestmen, a construction that bothers me a little. Why not “blind microharvestmen?” They are in fact eyeless, and they’re definitely micro. And they’re members of the arachnid order Opiliones, whose 5,000 species you probably know as daddy-longlegs. “Harvestman” is a British name, inspired by their tendency to show up in numbers during harvest season. The Brits also call them shepherd spiders; in parts of Mexico they’re pinacates; in Japan, mekuragumo. 

Although they have eight legs, harvestmen are not spiders. (It doesn’t help that some true spiders with attenuated legs are called daddy-longlegs spiders.) Spiders have waists, dividing head-and-thorax from abdomen; harvestmen have a one-piece ovoid body.  

Harvestmen don’t produce silk or spin webs. Spiders are predators; harvestmen eat plant matter and carrion as well as living prey. And male harvestmen (harvestpersons?) have a penis, whereas spiders do not. Male spiders do have a complicated work-around, involving portable webs and pedipalps, but let’s leave well enough alone here. 

Rick Vetter, an arachnologist at UC Riverside and a gold mine of spider lore, says there’s a widespread belief that harvestmen are deadly poisonous but can’t inflict lethal damage because their fangs are too short. This is a complete canard. They have no fangs or venom glands. Vetter also says the daddy-longlegs spiders, more properly known as pholcids, are not known to be biters and the venom they use on their prey has never been tested for toxicity to humans. 

The only way a harvestman could do you any damage is if taken internally. They repel predators by secreting unpleasant chemicals: Thomas Eisner, the pioneering chemical ecologist, found one in west Texas that produces benzoquinones in crystalline form. When provoked, it dilutes the crystals with saliva and uses the tips of its forelegs to brush the fluid on its attackers. This seems to discourage ants, at least.  

If microblind harvestmen have similar defenses, no one has reported it. We know very little about the lives of these creatures, in fact. They need microhabitats that provide high humidity, total darkness, and warmth; this usually means the underside of rocks. They prey on springtails, which are either primitive insects or not-quite-insects depending on which entomologist you listen to. They are not highly social, occurring mostly one to a rock, although groups of 10 or more have been observed. They show up when the rainy season begins and disappear when the ground beneath their rocks dries out.  

That’s pretty much their whole story. 

Blind harvestmen as a group are, one species excepted, found only in California. And the genus Microcina, the microblinds, occur only in the Bay Area, with a scattered distribution: one species near Mount Burdell in Marin County, one on the Tiburon Peninsula, two in the East Bay, one in Edgewood Park south of San Francisco, two in Santa Clara County. Each has been found in only a small patch of habitat at its respective site. Six of the seven species are limited to serpentine grassland, perhaps because serpentine-derived soil holds moisture like a sponge. 

Serpentine is weird stuff: our official state rock, formed on ancient seafloors and scraped onto continental margins when plates collide or microplates dock. Serpentine soil is chock full of magnesium, chromium, and nickel, lacking in nitrogen, potassium, and phosphorus. Most plants can’t tolerate the stuff. Some, though, grow there and nowhere else, like the bizarre Tiburon mariposa lily that blooms on Ring Mountain in late spring. There are outcrops of gray-green serpentine in most Bay Area counties; but only a few such locales have resident microblind harvestmen. 

How do these reclusive blind crawlers get around? If the seven species have a common ancestor, how did one set of descendants wind up on Mount Burdell and another in Edgewood Park? Are these the last survivors of a formerly more widespread population that lived in whatever a harvestman would consider flush times? The entomologists who named the genus, Thomas Briggs and Darrell Ubick of the California Academy of Sciences, were reasonably certain that each little enclave had a distinct species. It’s the penises. Each species has a uniquely-shaped organ, some tending toward the baroque; in one group, it folds and telescopes. If a Mount Burdell male were ever to meet an Edgewood female, their options would be limited. 

Six of the seven microblind harvestmen have a measure of federal protection: they’re covered in an omnibus Recovery Plan for Serpentine Soil Species, along with a couple dozen plants, a checkerspot butterfly, and a longhorn moth. The odd harvestman out is Berkeley’s own Microcina leei. Vincent Lee discovered it on the north side of Woolsey Canyon next to the Lawrence Berkeley Laboratory parking lot, beneath chunks of sandstone. No serpentine, so no Recovery Plan. A second population is or was found on Claremont Avenue northeast of its intersection with Ashby. No serpentine there either. 

It strikes me as grossly unfair that Lee’s microblind harvestman should be deprived of its Endangered Species Act rights because of a simple twist of geologic fate. If it’s even still there—I don’t know if anyone has gone back to look for it. Anyway, if anyone is searching for a cause to espouse, let me suggest Microcina leei. And what if it’s not a whale or a condor or a redwood? Nobody’s perfect.  

Which reminds me: thanks to Jim Buskirk for pointing out that the turtle whose photograph accompanied the March 1 article on the western pond turtle is actually a red-eared slider—a melanistic male. 


Photograph: Dr. Hays Cummins, Miami University  

Microblind harvestmen are members of the arachnid order Opiliones, whose 5,000 species you probably know as daddy-longlegs.?