At this time of year in temperate climes insect activity should be at it peak. Often, the insects themselves may be elusive, but evidence of their feverish activity is all around. In areas of woodland and scrub the leaves of many tree species, such as birch, oak and aspen are rolled into distinctive cigar shapes. These structures are the work of many different insects that construct these rolls either to hide in or as a nursery for their offspring. One such species is this small beetle, the birch leaf-rolling weevil (Deporaus betulae):
A female birch leaf rolling weevil (Deporaus betulae) just before she starts work on another leaf roll (Ross Piper).
This species rolls birch leaves into little nurseries for its offspring. What follows is a sequence of images showing how this 4-5mm beetle goes about doing this; a process that takes at least 1.5 hrs.
First off, the female selects a suitable leaf and then uses her mandibles to munch a wavy incision toward the mid-rib (Ross Piper).Next, she starts making another distinctive wavy cut away from the mid-rib, pausing for a while to chew the mid-rib a little in order to weaken it. Here, the industrious female gets on with the job in hand almost oblivious to the male trying to fertilise the egg she will lay in this particular leaf roll (Ross Piper).The last of the cutting is almost done regardless of the weight of the male (Ross Piper).Let the rolling begin. Using brute strength the female uses her legs to roll the leaf (Ross Piper).It’s difficult to see exactly how the female beetle rolls the leaf, but the cuts make it limp and therefore more flexible (Ross Piper).Almost there and the male is still clinging on tenaciously (Ross Piper).The next three images show the female tightening up the roll by getting in amongst the structure. At some point while inside the roll she lays a single egg (Ross Piper).The tightening of the roll continues (Ross Piper).The female puts the finishing touches to her ingenious brood chamber (Ross Piper).The completed roll, which took about 1.5 hours to make. The egg inside will eventually hatch and the larva will be surrounded by food and protected from many of its enemies. The fully grown larva will drop from its roll to pupate in the soil. Species that make leaf rolls for their eggs invest a lot of time and energy in this endeavour and because of how long it takes to make each roll they can only lay a relatively small number of eggs in their lifetime. However, each larva provisioned for and protected in this way has a much better chance of reaching adulthood (Ross Piper).
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