Sassy Frass: A Post about Poo

FRASS: debris or excrement produced by insects

Origin of FRASS: German, insect damage, literally, eating away, from Old High German vrāz food, from frezzan to devour. First Known Use: 1854

-Merriam Webster Dictionary

Caterpillar excreta is known as frass which is a combination of waste product and undigested plant material that has passed through the caterpillar gut.

Frass is a very handy way to identify that caterpillars are at work in your garden and can be one of the easier ways to locate larvae on a plant. If you find frass on the leaves of the plant, try looking on the branches directly above those leaves for the culprit. The shapes of scat of various species differ and are formed by the shape of the caterpillar gut.

Some species of skipper butterfly are capable of "scatapulting" or catapulting their frass away from their body. By pumping up their blood pressure these larva can shoot their poop away from their bodies with some species able to project their dung up to 4.2 feet. This odd behavior may help the caterpillar hide from predators that are attracted by the scent of droppings. Read more about “scatapulting” caterpillars at this National Geographic article.

In an enclosed setting, caterpillar spoor should be cleaned away every day. Wet stool is likely to grow mold which is unhealthy to caterpillars, also bacteria resident in the caterpillar gut may still be lurking in the poo. Caterpillars tiptoeing through the turds can be sickened by contact with mold and bacteria.

On the other hand, butterflies are designed to handle a liquid diet and are extremely efficient at digestion, leaving little behind for waste. Adult butterflies sip liquids through their proboscis and the food passes into the butterfly thorax. There the food is stored in an organ called a crop until it is digested in the midgut. During digestion nutrients from food are either absorbed into the blood or are stored as fats. Any liquid remaining from the process is generally reabsorbed in the rectum otherwise the butterflies may sometimes excrete small amounts of extra fluids.

When butterflies first emerge from chrysalis they excrete a fluid called miconium which is a waste product that builds up inside the pupa during the process of metamorphosis. This fluid causes the butterfly abdomen to appear swollen even after they have pumped up their wings, as shown in the picture of the Pipevine Swallowtail above.

A special tip of the hat to Mike K. who offered up the fun name for this icky little post.