Riddle for February

In the Pacific Ocean is an island about 100 by 100 meters in size. A scientific research team visits the island and places two insects there, each containing a dosage of an experimental drug. The scientists then leave, but the insects do quite well for themselves, as they have remarkable reproductive prowess thanks to the drug they have consumed. On the second day, they have already doubled and there are now four insects. On the third day, there are eight insects present, and so forth in this manner.

Later, the research team returns to their experiment, but cannot land the helicopter, as the island now has far too many insects for them to do so. They're able to deduct from their bird's eye view that just about half of the island is now covered with insects. As a matter of deciding whether or not to continue the experiment, they need to figure out how long it will be before the entire island is covered completely with the insects. If the scientists returned on the thirtieth day, how many more days will it take before the island is completely overrun by insects?

Answer (highlight to read): One. If the insects double each day, then a half-full island would be full the next day.