If the caterpillar population was wiped out by a disease, which population would experience an immediate decrease?

The population that would experience an immediate decrease is the eagle.

Explanation: Eagles often rely on a food source that includes small mammals and sometimes insects, such as caterpillars. If the caterpillar population is wiped out, it may impact the food web and reduce food availability for eagles, potentially leading to a decrease in their population as well. The other species listed (snail, rabbit, lizard, grass, bluebird) are less directly affected by the loss of caterpillars.