All bees are holometabolous insects. That’s a long way of saying they undergo complete metamorphosis. And that’s a long way of saying they have four life stages: egg, larva, pupa, and adult. Got it? Excellent! The rest is easy.
Like lots of similar insects, many bees spin a cocoon as they transition from a larva into a pupa. You may have seen the cocoons of mason bees which are firm and brown. Or you may have seen the cocoon of a butterfly or moth. In all cases, the cocoon safely seals the pupa from the outside world. But trapped inside, it cannot eat or defecate.
Eating and fasting stages
If you analyze the four life stages, you will see that the egg is a non-eating (fasting) stage. The egg is followed by the larva, which is an aggressive eating stage. Next, the pupa is the second fasting stage. After that, the adult is another eater. Clearly, the stages alternate between eating and using what was previously eaten.
To say larvae are aggressive eaters is something of an understatement. The larvae of butterflies and moths can mow crop plants to the ground. Right now, for example, cabbageworms, the larvae of the cabbage white butterfly, are devouring cole crops across the continent. Incredibly, about 85 percent of the worst crop pests are larval stages of some innocuous-looking insect. On the bright side, however, the larvae of the introduced cinnabar moth are chewing their way across pastures of tansy ragwort.
Larvae eat themselves silly
Honey bee larvae have equally voracious appetites. Some sources estimate that a honey bee larva increases its weight 1500 times in 5.5 days. That kind of growth requires serious munchies.
The food digested by the larvae is stored for use during the pupal stage when the bee transforms into an adult. Spinning the cocoon is one of the first things that happens as the larval stage comes to a close.
Rolling into a cocoon
Inside the newly capped brood cell, the larva does a somersault similar to the forward rolls you did in elementary school. As the bee rolls forward, it produces four substances. The silk glands, which are in the mouth, secrete a clear substance in long strands. In addition, three more substances are excreted from the anus: one is clear, one is yellowish, and one is feces.
As the larva somersaults within the brood cell, the cocoon materials exude from the bee’s body. But unlike a moth, butterfly, or solitary bee, the cocoon sticks to the inside of the brood cell. While you might imagine a butterfly cocoon being like a mummy case, the cocoon of a honey bee is more like wallpaper: they hang it up and leave it there.
Honey bee cocoons stay behind
After the pupa develops into an adult, the bee emerges from her natal cell, leaving the cocoon behind. Glued to the brood cell, the cocoon will not release. The feces is wrapped tightly within the other cocoon substances, nature’s way of assuring feces does not contaminate the inside of the brood cell.
Since the cocoons stick forever inside the comb, we never see a cocoon that looks anything like those produced by solitary bees or other insects. What we can see, however, is the forever darkening color of brood combs after successive generations of bees have left their cocoons and feces behind. The people who measure such things say that the inside of brood cells actually gets smaller over time, due to the build-up of multiple cocoons and metabolic waste.
Honey Bee Suite