On Sun, 9 May 2010 06:01:16 -0700 (PDT), Onetap
wrote:

Bee droppings, probably. On the first warm day after winter, they
emerge from the hives in large numbers and unload a whole winter's
worth of bee crap en-masse.
The first warm-enough day would have been some weeks ago. Probably
other insects leave similar yellow deposits as well. I believe they
may also rest on laundry to suck up moisture. Any hives nearby? Is it
under any trees (honey dew, aphid excreta)? Any flowering crops that
would place you under the bee flight-path?

While possible, that is far less likely at this time of year, it is
more common in February or March (you try holding it all in for three
or four months!) During the rest of the year I rarely see any voiding
- having a greenhouse right next to some of my hives and with a
regularly used washing line less than 10 feet away any voiding would
be really noticeable.

Returning foraging bees (carrying nectar/and or pollen) quite often
rest for a few minutes either to clean themselves up or just to get
their breath back before a final short flight to the hive, usually
this resting place will be within a few tens of feet of a hive. A bed
sheet on a washing line is a visible target and being grippy on a bee
scale it makes a good resting place. If there has been a dry spell
you can also get water carrying bees sucking up water from damp
washing, they might have a bit of pollen debris on their bodies.

Maybe my bees are better toilet trained and use the adjacent field,
but In twenty odd years of keeping bees, marking of washing hasn't
ever been a significant problem.
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