Monday 5 December 2011

How do bugs cope with winter?

We've had a couple of frosts in the last few days. Despite the die-hards which allow me to post occasionally these days, most insect species are nowhere to be seen throughout winter. How and where are bugs surviving the cold weather? There are various ways in which invertebrates go through the winter.
Far, far Away
Some - I'd say the lucky ones, avoid winter altogether - they are far, far away during winter, having migrated to warmer areas around the Mediterranean. These include several butterflies, moths, hoverflies and dragonflies (Red Admiral, Painted Lady -above - Silver Y and the Migrant Hawker are examples) which often lack a frost-resistant stage in their life cycle.
Slowing Down
Others stay to brave the elements, a few of them even carrying on more or less as normal, but at a much more sluggish pace. These are the invertebrates that enjoying the occasional sunbathing during rare winter sunny spells: Bluebottles (above), Winter Gnats, the window spider (Zygiella x-notata). Some moth caterpillars, like the Ruby Moth caterpillar, are found active in the middle of winter. A few bumblebee populations are starting to behave this way as the climate warms and they can make use of winter flowering resources.
Many insects enter a dormant state or diapause: this is the scientific term to describe what we often call 'hibernation': organisms enter a physiological state, dormancy or diapause, in which growth and feeding pretty much stop, and metabolism is very reduced. To protect their bodies against the damaging effects of freezing, some chemicals (glycerol and anti-freeze protein are two of them) are produced in their bodies to maintain cell stability and aid survival under low, often freezing, temperatures. Overwintering can occur in any stage of the life cycle depending on the species or taxonomic group  - egg, larva or nymph, pupae or adult (imago).
The beautiful blue silk cocoon of a Enoplognatha spider, ready for winter.
For example grasshoppers, aphids and many spiders overwinter as diapausing eggs. Many dragonflies and damselflies overwinter underwater as nymphs. Many solitary bees overwinter as pre-pupae in their nest cells.
A fully developed Noctua moth caterpillar in early spring
Some butterflies and flies overwinter as pupae, whereas some butterflies (Comma, Small Tortoiseshell, Brimstone), Ladybirds, queen wasps and queen bumblebees hibernate as adults. Many solitary bees are already imagos in their cells, waiting for the right time to emerge.
 I will keep my eyes open for bug life throughout the winter and be on the lookout for any stirrings indicating that springs is coming.

1 comment:

RayHolden said...

I am still finding female (but no male) Winter Moths, Harvestmen and early instar Forest bugs on the move on the walls of my local bus shelter.