Solitary wasp

According to mathematician Howard Eves in his book In Mathematical Circles:

A striking instance of what may be number sense in insects is illustrated by the so-called solitary wasp. The mother wasp lays her eggs individually in separate cells and then provides each cell with a number of live caterpillars on which the young feed when they hatch. The remarkable thing is that the number of caterpillars is surprisingly uniform for a given species of wasp - some species provide five per cell, others twelve, and still others as many as twenty-four. Most surprising is the genus eumenus, a variety in which the female is much larger than the male. Somehow or other, the mother wasp knows whether the egg will produce a female or a male grub; if the egg is female she provides its cell with ten caterpillars, if the egg is male she provides its cell with five.