Hibernating drone flies

It’s autumn and those creatures which hibernate through the winter are beginning to make their preparations. The squirrels are out burying nuts to tide them through, the bats are fattening up on insects to see them through torpor and those invertebrates which sleep the winter away are looking for safe places to stay.

A likely indicator of a hibernating insect is an early appearance in the spring. This is true of the brimstone butterflies which, for many, heralds the start of spring, and also the rather ungainly named drone fly. This is actually a hoverfly – Eristalis tenax – which is named not for the sound it makes in flight but for its similarity to a honey worker bee, a drone. These flies can often be seen early in the springtime, taking advantage of the first available nectar sources such as the lesser celandine pictured below.

Drone fly - Eristalis tenax - on a lesser celendine
Drone fly – Eristalis tenax – on a lesser celendine

We visited Tattershall Castle last weekend – a National Trust property out near Lincoln – and spotted several of these drone flies investigating crevices and cavities in the roof of the kitchen at the ground floor of the castle. You descend here down a small flight of steps and this movement below the ground will appeal to the hoverflies – conditions tend to be more stable and remain above freezing when you are beneath the ground level. Stability of conditions is often as important as suitable temperatures – a stable environment means less false signals that spring is here and emerging from hibernation too soon is never a good idea!

Drone fly investigating a hibernation site at Tattershall Castle
Drone fly investigating a hibernation site at Tattershall Castle

The hoverflies were not alone – tattered small tortoiseshells and red admiral butterflies were also checking up and down the walls for a safe place to roost for the winter whilst herald moths were already settled and looking set to sleep until spring.

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