NOVEMBER
2005

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

11-10-05

Some Insects are Waste Management Experts

If you are what you eat, some insects might have reason to worry! But don't worry about them, because, as far as we know, insects don't worry about things such as food habits. However, humans do have any number of worries, including how to group things. Animals, for instance. One way that biologists like to group animals is according to food that the animal consumes.

Insects are generally placed in one of three general categories, according to their food preferences. About half of all insect species feed on living plants. They are known as herbivores . Other insects chow down on living animals and are called carnivores. About 30 percent of the insect species fit into this category.

If you're keeping tabs on the percentages, this means that 20 percent of the insect species do not feed on either plants or animals. These insects feed on dead stuff. Of course, the dead stuff was once a plant or animal, but it is no longer living when the insect makes a meal of it. Scientifically, such insects are called saprophagous. They are nature's cleaner-uppers.

Saprophagous insects include deadwood-eating termites, roadkill animal-eating fly maggots and almost anything dead-eating cockroaches. This group also includes insects that feed on animal manure. Technically known as coprophages, they are the pooper-scoopers of the insect world.

If Kermit the Frog lamented about the difficulty of being green, just imagine how he might have felt if he had been a manure-eating insect, instead of an insect-eating frog. These insects are the Rodney Dangerfields of the insect world -- they get no respect! But what they eat helps define their ecological role, which is recycling animal wastes. And, if that role were not fulfilled, they would certainly be missed.

To the person who has just stepped in an animal scat -- the polite way of saying poop -- it is hard to imagine that manure-eating insects have trouble finding a meal. However, this is not the case for at least two reasons. One is that manure is not as readily available as it might seem. Take a cow on pasture, for example. Old bossy will drop about 12 pats per day, but they are spread out across the grazing area.

It is tempting to think that insects feeding on animal manure wouldn't have a lot of competition for their food. But that is not the case. There are a number of insects that spend their entire life dining on what comes out of the digestive system of other animals. And that's reason number two that feeding on manure is not an easy life.

So how do insects find a manure food source? Some fly around looking for such food and, in a bit of scientific information that is probably not much of a surprise to most of us, use odor to find it. A few insects actually follow the animal around until the inevitable happens and then take advantage of a fresh meal. Some cow-manure feeding flies do this. A few of these flies have been observed to be overly enthusiastic and, as a result, get clobbered by the meal before it hits the ground.

One of the most unusual approaches to finding a manure food source is exhibited by a moth. The caterpillar of this moth feeds on the feces of sloths. The moth rides on the sloth until it comes down from the trees to answer the call of nature. Then the moth lays eggs on the fresh manure.

Probably the most widely recognized of the insect manure-feeders are the dung beetles. This group of beetles includes some of the largest insects by weight, the goliath and Hercules beetles. All form a ball out of the manure. The ball is then rolled along the soil surface and buried in the ground where eggs are deposited on this ball of slightly used food.

Dung beetles are specialists. Each species only utilizes the manure of a specific type of mammal. In general, the size of the beetle corresponds to the size of the mammal that provides the manure. The biggest beetles, as you might guess, feed on elephant manure.

One interesting habit of the dung beetles is that they generally don't bury the manure balls that they manufacture. It seems that while a pair of beetles are digging a hole, other beetles are likely to steal the ball. The victims of this thievery then steal another ball. Eventually all the balls get buried. I guess you could say there is no honor among dung beetles. But before you criticize their lifestyle, you might ask this question: "Would you like to pack manure into little balls and roll them around all day?"

 

Writer: Tom Turpin
Editor: Olivia Maddox