Why can't you control the brown Treesnakes by using indigestible glass eggs or real eggs that have been laced with a poison?

First, snakes are extremely alert to the temperature, odor, and other chemical cues that help them discern real eggs from other objects that may be egg-shaped. Even if a snake were to ingest a glass egg it would probably regurgitate it when it proved indigestible. The idea of placing a poison (strychnine or other substances are often proposed) is also impractical for various reasons:

1. Snakes may not eat eggs that are not recently laid and hence accompanied by fresh odors or those that are being actively incubated (also distinguished by odors associated with the incubating bird and temperatures above the ambient temperature of the substrate where the egg is found);

2. Poisoned eggs are more likely to be found and ingested by unintended (nontarget) animals such as dogs, cats, pigs, or monitor lizards. The combination of low attraction to snakes and potential for unintentional effects on other animals makes all egg based baiting or control schemes impractical in real world contexts.