Nature Bulletin No. 77   August 3, 1946
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Supt. of Conservation

****:SCUM

In August we have our "Dog Days", so named by the ancient Romans 
because the bright blue star Sirius, the Dog Star, is then in ascension: 
rising with the sun. In the Dog Days, snakes went blind, dogs went mad, 
and humans were subject to fevers and malignant influences -- all 
foolish superstitions arising from the fact that Rome was a big 
unhealthy city surrounded by swamps.

We apply "Dog Days" to the hot humid period in August. In the Middle 
West it is good "corn weather". About this time, scum forms on the 
surface of the water in swamps, ponds and streams. Fly-fishermen curse 
it. Mothers refuse to let their kids go swimming in it. What is this 
scum?

There are two general kinds, both composed of small living plants. One 
kind is called duckweed or "duck meat" the smallest of the flowering 
plants. Each plant consists of a tiny, floating leaf, some as small as a 
pinhead, with 2 or 3 short thread-like roots dangling in the water. They 
multiply rapidly in hot weather. They have a tiny flower and set seed. 
Sometimes they completely cover small bays or even whole ponds. 
They drift with the wind and may pile up a foot deep on a windward 
shore. They are an important food for ducklings and certain adult 
species -- notably teal.

The other kind of scum is made up of a variety of still simpler, smaller 
Plants: algae, the most primitive form of plant life. Algae form scum 
because most of them grow in tangled masses of filaments which trap 
sufficient bubbles of the pure oxygen they produce in bright sunlight to 
make them rise to the surface. Some contain enough fat to float them.

Lake land plants, algae can thrive and grow only if they get sunshine 
and various substances dissolved in water. They form the base of a 
pyramid of food chains supporting practically everything that lives in 
water. Protozoa and water fleas live on algae; these are eaten by insect 
larvae and worms; these in turn are eaten by crayfish and minnows, 
which are eaten by such fish as bass and crappies.

Algae scum is the aquatic "staff of life. "