Doing the Math on German Cockroaches

As mentioned in a previous post, German cockroaches are not actually from Germany, but Asia. In fact, they are closely related to Oriental cockroaches. They are smaller (1/2-5/8 inch long) than some other species of cockroaches, and they live and hide easily indoors. But German roaches have an advantage over other varieties in their ability to reproduce in large numbers. Perhaps this is why they present such a challenge to homeowners and pest control management. In an effort to quantify the biological potential, lets do the math.

A basic formula for estimating how many roaches are produced per year from a pregnant female is to multiply the number of embryos per egg case by the number of egg cases produced per year. For instance, one pregnant American cockroach may have an average of 16 embryos in her egg capsule. If she lays 30 egg capsules, 16X30=480  mature adults in about a year. By contrast, if we start with one pregnant German cockroach that has an average of 30 embryos in her egg sack, and she lays 5 egg case, we would have 30X5=150 mature adults - in three months! If half the adults are female and they all mate, in 6 months we would have 75X30X5  mature adults. The number is now up to 11, 250, in half a year. If half those adults are female... you get the idea.  Saving you the math, one pregnant adult German cockroach could multiply into more than 63 million cockroaches in  a year, if left unchecked. Potentially, a German cockroach can out-produce an American cockroach by 131,000 times. 

Fortunately, we have management techniques to keep up with these common invaders. Insecticides that contain Insect Growth Regulators interrupt or inhibit the life cycle of the insect targeted. Sometimes called "birth control for roaches," these chemicals can be a valuable tool in limiting the biological potential of a cockroach population. If the bug can't reach adulthood, it can't reproduce. When combined with an adult cockroach killer, the results are significant. However, insecticides are most effective in controlling cockroaches when combined with sanitation and exclusion. Baits can also be useful, but are slow-acting and also require thorough cleaning to remove any other attractive food sources which may draw the bugs away from the bait. There is no easy or quick solution to a cockroach problem, but as the numbers indicate the best plan is to attack the problem before it becomes a nightmare - which in the case of German cockroaches, will happen quickly.