Color in the Meadow
1An old railroad line on the edge of town was turned into a walking and biking trail, and the strip of meadow beside it is now a county nature area. Keziah Morrow, an eighth grader, joined the county's summer science volunteers there. Their project was a small leaf beetle that lives on the meadow grass. In this population, some adult beetles are bright green and others are tan-brown.
2The county biologist explained that body color in this beetle is an inherited trait. In the county lab, pairs of brown beetles mostly had brown offspring, and pairs of green beetles mostly had green offspring. The lab also kept 40 adults in clear containers for their whole adult lives, and none of them changed color. Adults appear in late spring, feed on grass all summer and lay eggs on the ground in October. Females of both colors laid about the same number of eggs in the lab. The eggs hatch the next spring.
3The meadow changes with the seasons. In June the grass is fresh and green. By September, after the hot, dry weeks of late summer, most of it has turned tan. Songbirds such as sparrows hunt in the meadow and find insects mainly by sight.
4To test whether color affects how often birds attack the beetles, the volunteers made 100 clay models of beetles, all the same size and shape. They painted 50 green and 50 brown and pinned them to grass stems at evenly spaced spots across the meadow. After 3 days they counted the models with beak marks. They repeated the test with 100 fresh models in September, in the same spots and for the same number of days. The volunteers wore gloves when handling the clay and recorded results on a shared data sheet so each model was counted only once.
5The volunteers also counted live beetles in the same 20 sample plots twice. In early June they found 60 green and 40 brown beetles. In early October, just before egg laying, they found 18 green and 32 brown beetles. Keziah noticed that no new adults appear between June and October, so every beetle in the October count had survived the whole summer.