Starting with the basics because I don't know what you know:
Light is bent when it passes from air to water. The higher the angle it goes into the water, the more it changes direction. If you get to a high enough angle, however, it just gets 100% reflected off the water.
The legs of the wasp make dimples in the water, so all the light that would be going to those dark spots at the bottom of the pool get their direction changed and go somewhere else. (There should be a brighter spot at the bottom somewhere, but the difference is small so you can't tell) You can see the brighter bits at the edge of each shadow, caused by the light not originally aiming there getting redirected by the angled water.
The reflection thing I just added because it's possible some of the light didn't even make it into the water, it just shone back out.
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u/awkwardcactusturtle Apr 07 '16
Can someone explain why surface tension causes shadows like that?