Okay, it was only a glider. But it does get your attention! This sort of thing would never happen in a power plane, would it?
A few days ago we ran an airplane around the pattern following some major work. Several squawks were observed...including no airspeed. An obstruction, most likely an insect, was discovered in the pitot system.
Twice I've experienced pitot blockages in large airplanes, when the culprit was dead insects that swelled with contact with airborne moisture. Another occasion involved a considerable amount of water in the static system, courtesy of very large WWII sized static ports and a stiff, horizontal rain. It happens.
A variety of means of handling the problem can be had. Pitch and power works great...if you've got power. If not, then the power, not so much. You still have the sound of airflow over the cockpit. You have the feel of the controls. You have the angle the wing makes with the horizon, as well as indicated pitch (if you have an attitude indicator). You may find that your aircraft settles to a desired approach speed when you simply set the trim to a known setting, and relax the controls...trim pitch to fly the desired speed, and make slight adjustments. Approach a little high in the glider, slip as needed.
The day I received my new temporary flight instructor certificate, I climbed into my rented airplane to head home...and observed a tennis ball fitted neatly over my pitot tube...after takeoff. Here I was, a newly minted flight instructor, of all things, in the air with a tennis ball over my pitot tube. I flew home, parked not far from the flying club, and removed the tennis ball (pitot tube cover).
It happens. When it does, see it as a learning experience.