The snout or rostrum of a female Acorn weevil, Curculio glandium, is longer than that of the male. She uses it to chew holes in green acorns into which she deposits one or more eggs using a specialised organ. This organ, the ovipositor, is located at the end of her abdomen (body): it is a long, narrow, retractable tube which is remarkable by having both smell and taste receptors which can determine whether that acorn is a suitable food source for her developing larvae.
Once laid, an egg is naturally protected when the plant’s tissues heal the damaged outer shell of the acorn and seals the entrance to the hole. After hatching, the emerging larva feeds on the endosperm (the food store of the acorn). Following the fall of the fruit from the oak tree in early Autumn, the larva chews its way out of the acorn and tunnels into the soil where it remains overwinter in an earthen chamber.
Survival for several days during sub-zero conditions in winter (by a process known as ‘freeze avoidance’) is possible by the lowering of the temperature threshold at which the supercooled liquid in the body of the insect changes into the solid, ice, state by the production of chemicals like glycerol and glycol. The larva remains underground for one or two years before pupating - finally emerging as an adult during spring and summer months.
