Insect Engineers

Football-sized bald-faced hornet nests, hanging from branches, are prominent in the winter landscape.

January 10, 2020 | | Notes from the Wild

Winter is a good time to appreciate the remarkable engineering feats of insects. After leaves fall, galls, cocoons and wasp nests become more obvious.

Football-sized bald-faced hornet nests, hanging from branches, are prominent in the winter landscape. Grey paper walls enclose tiers of hexagonal cells that serve as brood chambers for the colony.

Bald faced hornet nests. Photo by Don Scallen.

Bald faced hornet nests. Photo by Don Scallen.

On a quiet summer’s day, it’s possible to hear hornets rasping wood with their sharp mandibles to gather the fibre that they combine with saliva to form pulp and make paper. I wonder if, long ago, this industry may have inspired paper making in our own species.

Winter nests are derelict and will not be used again. All the workers – hundreds or thousands – are dead. Queens are hunkered down in sheltered spots, waiting out the winter.

Cecropia moth cocoon. Photo by Don Scallen.

Cecropia moth cocoon. Photo by Don Scallen.

Cecropia cocoon. Photo by Don Scallen.

Cecropia cocoon. Photo by Don Scallen.

Other insect structures more easily noticeable in winter are cocoons. The largest cocoons, usually affixed to tree branches, are those of the magnificent cecropia moths. Cecropia caterpillars make them by exuding silken fibres from their mouths. These cocoons are tough, offering excellent protection from weather and predators.

Within these cocoons the caterpillars form pupae and lie dormant till spring. Then the moths squirm out of one end of the cocoon and cling to branches while their wings harden in preparation for flight.

It takes goldenrod gall flies less work than either moths or hornets to create their protective structures. Eggs inserted into the stems of goldenrod hatch into small grubs. As the grubs feed, they stimulate the goldenrod to grow thick-walled protective orbs around them.

Goldenrod gall. Photo by Don Scallen.

Goldenrod gall. Photo by Don Scallen.

Goldenrod gall predated. Photo by Don Scallen.

Goldenrod gall predated. Photo by Don Scallen.

Goldenrod gall fly larva in opened gall. Photo by Don Scallen.

Goldenrod gall fly larva in opened gall. Photo by Don Scallen.

Downy woodpecker. Photo by Don Scallen.

Downy woodpecker. Photo by Don Scallen.

Snug within these orbs, the gall fly larvae pass the winter – if they are lucky. Chickadees and downy woodpeckers know the secret of these galls. They chisel into them and eat the grubs.

Insects are now quiescent, but evidence of their dominion can still be found throughout our fields and forests.

About the Author More by Don Scallen

Don Scallen enjoys sharing his love of nature through his writing and presentations. Check out his blog "Notes from the Wild".

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