Chapter 4, Problem 88PP

Caterpillar Pellets

The larvae (caterpillars) of certain species of butterflies and moths construct shelters on a host plant out of folded or rolled leaves secured with silk threads. Many of those types of caterpillars eliminate waste by ejecting fecal pellets (frass) at high speeds so that the pellets are projected far away from the caterpillar and its shelter. Various explanations for this behavior have been proposed, but some studies have shown that it may help keep predatory insects such as wasps from locating the caterpillars by homing in on the odor of caterpillar frass.

Video microscopy has been used to study the pellet ejection process In one study, the video images reveal that a group of Brazilian skipper caterpillars that are about 50 mm long eject pellets at angles between 10° and 40° above the horizontal. There is no correlation between the size of the pellet and the angle at which it is ejected, but larger pellets are shot with lower speeds, as shown in Figure 4-35. The pellets are small and dense enough that at the speeds at which they travel air resistance is negligible.

Figure 4-35

Problem 88, 89, 90 and 91

88. • If pellets shot at the same angle are compared, which of the following is true?

1. A.    A lighter pellet travels farther because of its higher ejection speed.
2. B.     A heavier pellet travels farther because it is launched more horizontally.
3. C.     Pellets of all masses travel equally far because the launch angle is the same.